Added PHP.ug to the websites-section

On PHP.ug you can find an overview of all PHP-Usergroups known to the maintainers. It's also the source of the usergoup-list on php.net/ug.php
Change link caption of cebe/markdown

I choose this name instead of just "Markdown" to make it more distinguishable.

Thanks fore mentioning it here, btw :)
Adding ProxyManager to data-mapping section
Update README.md
Added PHP Internals Book
Merge pull request #149 from aminemat/master

Added PHP Internals Book
Move Interals Book up list.
Merge pull request #145 from olso/master

added Deployer
Undo accidental merge.
Merge pull request #112 from heiglandreas/master

Added PHP.ug to the websites-section
Tweak description and title.
Merge pull request #125 from cebe/patch-1

Change link caption of cebe/markdown
Tweak description and title.
Merge pull request #144 from Ocramius/patch-1

Adding ProxyManager to data-mapping section
Description tweak.
Tweak contribution guidelines, and add info about trailing whitespace.
Remove monthly suggestion ticket line.
Add phpDox
Update CONTRIBUTING.md

Fixed spelling
Merge pull request #158 from akullpp/patch-1

Update CONTRIBUTING.md