add ktlint rules for code style guideline

Author: oguz.celik

README.md

@@ -3,7 +3,7 @@ List of Architecture and code guidelines at Trendyol when developing for Android
 
 * [Package Guideline](package_guideline/package_guideline.md)
 * [App Architecture Guideline](README.md)
-* [Code Style Guideline](README.md)
+* [Code Style Guideline](code_style_guideline/code_style_guideline.md)
 * [Gradle Guideline](README.md)
 * [Analytics Architecture Guideline](README.md)
 * [Resources Naming Guideline](resource_naming_guideline/resource_naming_guideline.md)

code_style_guideline/.DS_Store

@@ -0,0 +1,20 @@
+## Kotlin Rules
+
+- 4 spaces for indentation
+- No semicolons (unless used to separate multiple statements on the same line)
+- No wildcard / unused `import`s
+- No consecutive blank lines
+- No blank lines before `}`
+- No trailing whitespaces
+- No `Unit` returns (`fun fn {}` instead of `fun fn: Unit {}`)
+- No empty (`{}`) class bodies
+- No spaces around range (`..`) operator
+- No newline before (binary) `+` & `-`, `*`, `/`, `%`, `&&`, `||`
+- When wrapping chained calls `.`, `?.` and `?:` should be placed on the next line
+- When a line is broken at an assignment (`=`) operator the break comes after the symbol
+- When class/function signature doesn't fit on a single line, each parameter must be on a separate line
+- Consistent string templates (`$v` instead of `${v}`, `${p.v}` instead of `${p.v.toString()}`)
+- Consistent order of modifiers
+- Consistent spacing after keywords, commas; around colons, curly braces, parens, infix operators, comments, etc
+
+These are the [default rules for ktlint](https://github.com/shyiko/ktlint/blob/master/README.md#standard-rules)