Attempted fix for build issues on Linux with RubyGems 2.0.0

On Linux the build is failing with:

  make install
  /usr/bin/install -c -m 0755 wikitext.so /data/shared/bundle/ruby/2.0.0/gems/wikitext-4.0/ext
  /usr/bin/install: `wikitext.so' and `/data/shared/bundle/ruby/2.0.0/gems/wikitext-4.0/ext/wikitext.so' are the same file

Looks to affect many gems with native components:

  https://github.com/rubygems/rubygems/issues/411
  https://bugs.ruby-lang.org/issues/7344
  https://bugs.ruby-lang.org/issues/7698

The workaround applied here is to move the extension files down one
level in the hierarchy.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Prep for 4.0.1 release

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Bump version number post-release

Signed-off-by: Wincent Colaiuta <win@wincent.com>