Adding ModifiedFile.content and deprecating ModifiedFile.source_code

[stefanodallapalma]

This pull request should address #216, open to discuss modifications and refactoring operations.

I believe source_code is a core property used by many and therefore should not be refactored to content any time soon. Instead, it should be deprecated and then removed in a future version of PyDriller. Therefore, this pull request addresses issue #216 by adding the class variables content and content_before that behave exactly like source_code and source_code_before; the latter have been also translated to properties to warn the user about their deprecation.

Test cases using property source_code and source_code_before. Checked ☑️ if modified for DeprecationWarning and testing the new property content:

• tests/test_commit/test_source_code_before()
• tests/test_commit/test_source_code_before_complete()
• tests/test_commit/test_filename()
• tests/test_commit/test_metrics_python()
• tests/test_commit/test_metrics_cpp()
• tests/test_commit/test_metrics_java()
• tests/test_commit/test_metrics_not_supported_file()
• tests/test_git_repository/test_should_detail_a_commit()

Methods in ModifiedFile that use source_code or source_code_before. Checked ☑️ if modified to warn deprecation and to include the new property content:

• init()
• self.source_code has been renamed to self.__source_code to handle DeprecationWarning in a new method/property source_code().
• self.source_code_before has been renamed to self.__source_code_before to handle DeprecationWarning in a new method/property source_code_before().
• Added self.content and self.content_before.
• hash()
• self.source_code replaced by self.content to generate hashable string.
• _calculate_metrics()
• Refactor source_code and source_code_before to content and content_before.

Methods in Commit that use source_code or source_code_before.

• _parse_diff()
• Added key:value pairs content_before and content to the diff_and_sc dictionary that is passed to ModifiedFile.

Future refactoring:

• Rename diff_and_sc -> diff_and_content in commit.py.

[codecov]

Codecov Report

Merging #220 (fd76387) into master (58ae15e) will decrease coverage by 0.16%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##           master     #220      +/-   ##
==========================================
- Coverage   98.34%   98.18%   -0.17%     
==========================================
  Files          15       15              
  Lines        1028     1045      +17     
==========================================
+ Hits         1011     1026      +15     
- Misses         17       19       +2     

Impacted Files	Coverage Δ
pydriller/domain/commit.py	98.18% <90.00%> (-0.46%)	⬇️

[ishepard]

LGTM! Thanks for making the change!