Improve support for tag files generated with stable ctags

When tags don't have namespace information use just the name for matching
in various contexts. This might result in incorrect answers but still more
useful as do nothing when the tags file generated with unpatched ctags
against a codebase with namespaces.
Related to #5, #4
Move built-in information to one file

This should reduce the IO load on the first load and makes it easier
to create a single file bundle, related to #5
Change default for g:phpcomplete_complete_for_unknown_classes

This completion is pretty much useless, i find it better to have the
plugin fail fast, than make the user wait for a huge and highly inaccurate
list of completions.
Added g:phpcomplete_search_tags_for_variables option

With this option you can enable/disable variable searches in tags.
These result usually yield highly inaccurate results but have the
potential of being awful slow. Disabled by default.