Fixed compile error in CocoaHTTPServer submodule

Xcode 4.6 found an uninitialized-variable error, so CocoaHTTPServer now fails
to compile. The fix was simple but to be able to make a change I had to fork
CocoaHTTPServer, so I've changed the submodule's URL.

** You need to run "git submodule sync" after pulling this fix **
Expose filter compilers in public API

Unexpectedly difficult because I had to unify the public CBLFilterBlock
with the underlying CBL_FilterBlock (and the same for validation blocks,
while I was at it.)
Merged CBL_DatabaseManager into CBLManager.
Finished renaming CBL_DatabaseManager to CBLManager.

This continues the previous commit; this one's just a search/replace.
Clean up binding of CBL_Database to CBLDatabase

* CBL_Database.touchDatabase renamed to .publicDatabase
* .publicDatabase accessor now instantiates the CBLDatabase on demand
* CBL_Database now knows its CBLManager (needed to implement the above)
API cleanup: enable better compile-time checks

* Use 'instancetype' instead of 'id' as return type where appropriate.
* Add 'nonnull' attribute, to flag pointer params that can't be null
  (only in public API and CBLMisc so far)
Merged CBL_View into CBLView.
Finished renaming CBL_View to CBLView.

This continues the previous commit; this one's just a search/replace.