Removed unused code
Removed outdated documentation
Always use GIT_HASHSIG_SMART_WHITESPACE when diffing for merges

git_merge_tree_flag_t cannot contain any GIT_DIFF_FIND_xxx flags so there's not point in checking for them
Properly handle errors from git_hashsig_compare()
Replaced git_hashsig_option_t by git_hashsig_flags
Added cl_git_rmfile()
Added GIT_HASHSIG_ALLOW_SMALL_FILES to allow computing signatures for small files

The implementation of the hashsig API disallow computing a signature on small files containing fewer than a few lines. This new flag disables this behavior.

git_diff_find_similar() sets this flag by default which means that rename / copy detection of small files will now work. This in turn affects the behavior of the git_status and git_blame APIs which will now detect rename of small files assuming the right options are passed.