Support removed files

[sedrik]

I just found out that erlgit currently does not support removed files.

escript: exception error: no function clause matching git:change_type("R ") (src/git.erl, line 297)
  in function  git:'-status_changed_files/2-lc$^0/1-0-'/2 (src/git.erl, line 315)
  in call from git:'-status_changed_files/2-lc$^0/1-0-'/2 (src/git.erl, line 316)
  in call from cgit_util_core:changed_erl_files/0 (src/cgit_util_core.erl, line 49)
  in call from cgit_util_core:eunit/0 (src/cgit_util_core.erl, line 9)
  in call from gen_script:run/3 (src/gen_script.erl, line 64)