This PR fixes #225.

For example, the VersionInfo.bump_major() method calls semver.parse_version_info and semver.bump_major instead of having its own implementation. This has several drawbacks:

• the VersionInfo class depends on other, "remote" function outside the class.
• the class is not "self-contained".
• it makes deprecating module level functions (and removing them) harder because of these dependencies.

As such, I had to move some implementation into the VersionInfo class. With this approach, we can deprecate the module level function without triggering a false positive when calling a method in VersionInfo.

This PR contains the following changes:

• Add test cases

  • Test also missing finalize_version
  • Test the warning more thouroughly with pytest.warns instead of just pytest.deprecated_call

• In setup.cfg, add deprecation warnings filter for pytest

• Implement DeprecationWarning with warnings module and the new decorator deprecated

• Output a DeprecationWarning for the following functions:

  • semver.bump_{major,minor,patch,prerelease,build}
  • semver.finalize_version
  • semver.format_version
  • semver.parse
  • semver.parse_version_info
  • semver.replace

• Move module level implementation into VersionInfo

  • Move implementations:

    • semver.format_version -> semver.VersionInfo.format_version semver.VersionInfo.__str__
    • Move _REGEX into VersionInfo class
    • Move _LAST_NUMBER into VersionInfo class
    • Move also _increment_string and implement it as a staticmethod
    • semver.parse -> semver.VersionInfo.parse
    • semver.bump_* -> semver.VersionInfo.bump_*

  • Change implementation by calling VersionInfo methods (and not the other way around):

    • semver.compare
    • semver.finalize_version
    • semver.replace
    • semver.parse_version_info

• Introduce new public functions:

  • semver.VersionInfo.to_dict (from former _asdict)
  • semver.VersionInfo.to_tuple (from former _astuple)
  • Keep _asdict and _astuple as a (deprecated) function for compatibility reasons

• Update CHANGELOG.rst

• Update usage documentation:
  - Move some information to make them more useful for the reader
  - Add deprecation warning
  - Explain how to replace deprecated functions
  - Explain how to display deprecation warnings from semver

• Improve documentation of deprecated functions

  • List deprecated module level functions
  • Make recommendation and show equivalent code
  • Mention that deprecated functions will be replaced in semver 3. That means, all deprecated function will be still available in semver 2.x.y.

@gsakkis As you were also involved, I'd like to hear your opinion too. 😉