added doc files

docs/guide/caching.md

+Caching
+=======
+

docs/guide/error.md

+Error Handling
+==============
+

docs/guide/installation.md

@@ -34,7 +34,7 @@ Recommended Apache Configuration
 --------------------------------
 
 Yii is ready to work with a default Apache web server configuration.
-The `.htaccess` files in Yii framework and application folders restrict
+The `.htaccess` files in Yii framework and application folders deny
 access to the restricted resources. To hide the bootstrap file (usually `index.php`)
 in your URLs you can add `mod_rewrite` instructions to the `.htaccess` file
 in your document root or to the virtual host configuration:
@@ -108,4 +108,5 @@ server {
 }
 ~~~
 
-Using this configuration you can set `cgi.fix_pathinfo=0` in php.ini to avoid many unnecessary system stat() calls.
+Using this configuration you can set `cgi.fix_pathinfo=0` in php.ini to avoid
+many unnecessary system `stat()` calls.

docs/guide/migration.md

+Database Migration
+==================
+

docs/guide/mvc.md

@@ -11,7 +11,7 @@ the communication between the model and the view.
 
 Besides implementing MVC, Yii also introduces a front-controller, called
 `Application`, which encapsulates the execution context for the processing
-of a request.  Application collects some information about a user request and
+of a request. Application collects information about a user request and
 then dispatches it to an appropriate controller for further handling.
 
 The following diagram shows the static structure of a Yii application:
@@ -21,6 +21,7 @@ The following diagram shows the static structure of a Yii application:
 
 A Typical Workflow
 ------------------
+
 The following diagram shows a typical workflow of a Yii application when
 it is handling a user request:
 

docs/guide/url.md

+URL Management
+==============
+