vector: Add REMOVE, ADD_SORTED and RESET macros

Based on feedback from Corey Farrell and Y Ateya, a few new
macros have been added...

AST_VECTOR_REMOVE which takes a parameter to indicate if
order should be preserved.

AST_VECTOR_ADD_SORTED which adds an element to
a sorted vector.

AST_VECTOR_RESET which cleans all elements from the vector
leaving the storage intact.

Change-Id: I41d32dbdf7137e0557134efeff9f9f1064b58d14