added contribution guidelines
cleaned up whitespace
Reworked file/directory ignore functionality.

Now it's possible to ignore relative directories and
file patterns as well as absolute. .svn and .cvs dirs
are ignored out of the box. Absolute patterns should
start will a leading '/', otherwise a pattern is
considered relative. There might be some performance
implications at this point, hopefully most users will
not be affected by them.
cleaned up the code in projectile-index-directory
Removed project-ignored-extension-p.

Now that projectile supports relative ignores, the
functionality of project-ignored-extension-p is no
longer needed. Just add something like *.ext to
your .projectile file.
many documentation style fixes
updated Projectile's menu to reflect recent additions
added a missing space to the recentf prompt