solved error with functions for foreach
pop results to prevent stack pollution
extended diff and implmented diff:print

fixed error in commit.c
implemented find_similar

options are not implemented yet
implemented a type parameter for git_diff_num_deltas
Stubs for Index functions
added creation and destruction of index objects
read and write functions of the index.

write_tree_to is included in write_tree
entrycount and clear
added index functions and completed diff with index
more functions

added macro to handle errors