Add tests Git Log for Entities

[carlosparadis]

Tests for #79

Some cases to be moved to tests:

on APR:

    #git_log_commit <- project_git_log[572,.(file,data.commit)]
    #git_log_commit <- project_git_log[1872,.(file,data.commit)]

    # Some commit hashes, like APR's project git 572
    # throws error 128 from git
    # 6154ab7b1e862927c90ae6afa4dc6c57ee657ceb

    # This example changes function signature and a line inside
    # https://github.com/apache/apr/commit/ffdad353ac4b4bc2868603338e8ca50db90923a8

  #17000:18000 has a weird case of empty git blame
  # problem exist on row 17530 # cartesian product problem
  # project_git_log[17488] NA problem is a case when the file is deleted
  # see https://github.com/apache/apr/commit/cf9339bca711318261641ed70c6ee2543659b71b

Example deleted file: https://github.com/apache/apr/commit/cf9339bca711318261641ed70c6ee2543659b71b#diff-655f5b1366e2280b15aecbe9d440f845