[SocketClient] Remove ConnectorInterface::createUdp

It does not make sense to represent UDP as a stream. Streams have end
semantics, UDP does not.
[SocketClient] Rename Connector::createTcp to Connector::create
CS
Disable libev on travis

It's currently failing with strange build errors.
Update deps
Merge branch 'master' into travis-disable-libev

* master:
  Update deps
  CS
Move libevent and libev form require-dev to suggest
Merge branch 'refs/heads/travis-disable-libev'
Add travis build on PHP 5.5, allow failure
Build libevent extension instead of using pecl
Merge remote-tracking branch 'romainneutron/travis-php-5.5'

* romainneutron/travis-php-5.5:
  Build libevent extension instead of using pecl
  Add travis build on PHP 5.5, allow failure
Add note of child README docs to main README