Add nulls, and more newdecl and type system features.

New null_t type has a constant "null", which can be assigned to objects.
Methodmaps can now be "nullable", accepting null_t types.
The delete keyword now zaps non-const lvalue inputs.
Fixed some newdecl arguments not accepting references.
Allow functag matching to coerce arguments and return values.
Allow functags to accept new-style types as a return value.
Merge branch 'master' into nullable
Fix AMBuildScript compatibility issue with older objdirs.
Rename the null tag to null_t.
Allow CloseHandle() on nulls.
Port some includes to transitional API.
Port nominations.sp to the transitional syntax and API.
Mark the expression before flushing the staging buffer.
Fix some menu API oddities.
Remove VoteInProgress from Menu map.
Fix usage of `class` keyword in some includes.
Merge pull request #70 from VoiDeD/classname-no-world-entity

GetEntityClassname should handle the case where the world entity has not been created yet (r=psychonic).
Merge pull request #78 from VoiDeD/class-keyword

Fix usage of `class` keyword in some includes.
Merge pull request #73 from alliedmodders/nullable

Add nullable types and tighten up some new type system semantics.
Add setters and fix some methodmap bugs.
Merge branch 'master' into noms
Use setters.
Merge branch 'master' into redo-noms
Update nominations.sp and improve compiler error messaging.
Merge pull request #72 from VoiDeD/keyvalue-from-string

Implement StringToKeyValues.