convert lvgl from submodule to a plain old directory

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diff --git a/lib/lvgl b/lib/lvgl
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-Subproject 0732400e7b564dd0e7dc4a924619d8e19c5b23a
diff --git a/lib/lvgl/docs/CODING_STYLE.md b/lib/lvgl/docs/CODING_STYLE.md
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+# Coding style
+
+## File format
+Use [misc/lv_templ.c](https://github.com/lvgl/lvgl/blob/master/src/misc/lv_templ.c) and [misc/lv_templ.h](https://github.com/lvgl/lvgl/blob/master/src/misc/lv_templ.h)
+
+## Naming conventions
+* Words are separated by '_'
+* In variable and function names use only lower case letters (e.g. *height_tmp*)
+* In enums and defines use only upper case letters (e.g. *e.g. MAX_LINE_NUM*)
+* Global names (API):
+  * start with *lv*
+  * followed by module name: *btn*, *label*, *style* etc.
+  * followed by the action (for functions): *set*, *get*, *refr* etc.
+  * closed with the subject: *name*, *size*, *state* etc.
+* Typedefs
+  * prefer `typedef struct` and `typedef enum` instead of  `struct name` and `enum name`
+  * always end `typedef struct` and `typedef enum` type names with `_t`
+* Abbreviations:
+  * Only words longer or equal than 6 characters can be abbreviated.
+  * Abbreviate only if it makes the word at least half as long
+  * Use only very straightforward and well-known abbreviations (e.g. pos: position, def: default, btn: button)
+
+## Coding guide
+* Functions:
+  * Try to write function shorter than is 50 lines
+  * Always shorter than 200 lines (except very straightforwards)
+* Variables:
+  * One line, one declaration (BAD: char x, y;)
+  * Use `<stdint.h>` (*uint8_t*, *int32_t* etc)
+  * Declare variables where needed (not all at function start)
+  * Use the smallest required scope
+  * Variables in a file (outside functions) are always *static*
+  * Do not use global variables (use functions to set/get static variables)
+
+## Comments
+Before every function have a comment like this:
+
+```c
+/**
+ * Return with the screen of an object
+ * @param obj pointer to an object
+ * @return pointer to a screen
+ */
+lv_obj_t * lv_obj_get_scr(lv_obj_t * obj);
+```
+
+Always use `/*Something*/` format and NOT `//Something`
+
+Write readable code to avoid descriptive comments like:
+`x++; /*Add 1 to x*/`.
+The code should show clearly what you are doing.
+
+You should write **why** have you done this:
+`x++; /*Because of closing '\0' of the string*/`
+
+Short "code summaries" of a few lines are accepted. E.g. `/*Calculate the new coordinates*/`
+
+In comments use \` \` when referring to a variable. E.g. ``/*Update the value of `x_act`*/``
+
+### Formatting
+Here is example to show bracket placing and using of white spaces:
+```c
+/**
+ * Set a new text for a label. Memory will be allocated to store the text by the label.
+ * @param label pointer to a label object
+ * @param text '\0' terminated character string. NULL to refresh with the current text.
+ */
+void lv_label_set_text(lv_obj_t * label, const char * text)
+{   /*Main brackets of functions in new line*/
+
+    if(label == NULL) return; /*No bracket only if the command is inline with the if statement*/
+
+    lv_obj_inv(label);
+
+    lv_label_ext_t * ext = lv_obj_get_ext(label);
+
+    /*Comment before a section*/
+    if(text == ext->txt || text == NULL) {  /*Bracket of statements start inline*/
+        lv_label_refr_text(label);
+        return;
+    }
+
+    ...
+}
+```
+
+Use 4 spaces indentation instead of tab.
+
+You can use **astyle** to format the code. Run `code-formatter.sh` from the `scrips` folder.
+
+#### pre-commit
+
+[pre-commit](https://pre-commit.com/) is a multi-language package manager for pre-commit hooks.
+See the [instalation guide](https://pre-commit.com/#installation) to get pre-commit python package
+installed into your development machine.
+
+Once you have `pre-commit` installed you will need to [set up the git hook scripts](https://pre-commit.com/#3-install-the-git-hook-scripts) with:
+```console
+pre-commit install
+```
+
+now `pre-commit` will run automatically on `git commit`!
+
+##### Hooks
+
+The `format-source` local hook (see `.pre-commit-config.yaml`) runs **astyle** on all the staged source and header
+files (that are not excluded, see `exclude` key of the hook configuration) before entering the commit message,
+if any file gets formatted by **astyle** you will need to add the change to the staging area and run `git commit` again.
+
+The `trailing-whitespace` hook fixes trailing whitespaces on all of the files.
+
+##### Skipping hooks
+
+If you want to skip any particular hook you can do so with:
+```console
+SKIP=name-of-the-hook git commit
+```
+
+##### Testing hooks
+
+It's no necessary to do a commit to test the hooks, you can test hooks by adding the files into the staging area and run:
+```console
+pre-commit run name-of-the-hook
+```
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