Add CODECONVENTIONS, and modify i2c module to conform.

CODECONVENTIONS.md

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+Code conventions
+================
+
+When writing new code, please adhere to the following conventions.
+
+White space:
+- Expand tabs to 4 spaces.
+- Don't leave trailing whitespace at the end of a line.
+- For control blocks (if, for, while), put 1 space between the
+  keyword and the opening parenthesis.
+- Put 1 space after a comma, and 1 space around operators.
+
+Braces: 
+- Use braces for all blocks, even no-line and single-line pieces of
+  code.
+- Put opening braces on the end of the line it belongs to, not on
+  a new line.
+- For else-statements, put the else on the same line as the previous
+  closing brace.
+
+Include directives:
+- Don't include within a header file.
+
+Type names and declarations:
+- When defining a type, put '_t' after it.
+
+Examples
+--------
+
+Braces and spaces:
+
+    int foo(int x, int y) {
+        if (x < y) {
+            foo(y, x);
+        } else {
+            foo(x + 1, y - 1);
+        }
+
+        for (int i = 0; i < x; i++) {
+        }
+    }
+
+Type declarations:
+
+    typedef struct _my_struct_t {
+        int member;
+        void *data;
+    } my_struct_t;