Add support for .yml extension.
Move virtual filesystem check out of loop.

Thanks to Emmanuel Touzery.
Move virtual filesystem test to more logical place.
Ignore irregular files.
Refactor and fix bug.

The bug prevented vim-rooter identifying the project root directory when
using a file pattern and already at the project root.
Use markers.
Option to change directory for non-project files.
Improved Windows paths handling

Using something like substitute(..., '.svn/', '') to strip last
component of path caused a do-nothing operation on Windows, where path
components are separated by '\\'.  This lead to :cd to '.svn' directory,
instead of that one level up.

The fix consist of using fnamemodify(..., ':h:h') in place of
substitute(..., '.svn/', '').
Tighten up whitespace.
Look for .git before .git/ to work better with submodules.
Clarify the ordering of patterns.
Add a help file
Added doc/tags to .gitignore