Implement #139: Bump version inside VersionInfo

[tomschr]

This PR implements #139

• Add bump_major, bump_minor, bump_patch, bump_prerelease and bump_build as methods in class VersionInfo. With this methods, it is now possible to write something like this:

  ver = semver.parse_version_info("3.4.5")
  new_ver = ver.bump_major().bump_minor()

• Add test cases

---

Some comments about this implementation:

• I (re)used the module functions semver.bump_major() etc. to avoid implementing the same code (double code is bad code).
• It may be not as efficient as it could be, because it converts the VersionInfo into a string, bumps it, and convert is back into VersionInfo. Not sure if there is a better way to do it.
• I've created a "Draft pull request" so we can discuss and improve the code. ;-)

@ppkt Karol, what do you think? :-)

[ppkt]

Thanks for quick PR :) I have only small remarks regarding docstrings

[tomschr]

@ppkt I've implemented your suggestion in the above commits. Hope you are fine with that. 😉 Let me know if you prefer to squash the commits.

By the way: what amount of lines do I need to change to qualify for the contributors file? 😉

[tomschr]

Another question about consistency.

I've found out that some docstring are written differently. Some docstrings have this style:

def parse(version):
    """Parse version to major, minor, patch, pre-release, build parts.

    :param version: version string
    :return: dictionary with the keys 'build', 'major', 'minor', 'patch',
             and 'prerelease'. The prerelease or build keys can be None
             if not provided
    :rtype: dict

    >>> import semver
    >>> ver = semver.parse('3.4.5-pre.2+build.4')
    >>> # [...]
    """

while others have this style:

def bump_major(self):
        """Raise the major part of the version, return a new object
           but leave self untouched

        :return: new object with the raised major part
        :rtype: VersionInfo

        >>> import semver
        >>> ver = semver.parse_version_info("3.4.5")
        >>> ver.bump_major()
        VersionInfo(major=4, minor=0, patch=0, prerelease=None, build=None)
        """

Probably that was me to blame. 😢 To summarize: either we write doctests first and then all parameters, or vice versa. Is there any preferred style?

IMHO, at least we should be consistent. I would like to fix that, but that's probably something for a different PR, right?

[scls19fr]

Thanks @tomschr for this PR and @ppkt for this review.

[ppkt]

@tomschr I think you can update docstrings in separate PR. Regarding "contributors" file - I don't think there is any limit - feel free to add yourself. And thank you for your PRs :)

[tomschr]

@ppkt Ok, will attack consistency of docstrings in another PR. 😉 Regarding contributors file, I will add myself in one of my open PRs. 😄 Thanks!

[scls19fr]

This PR helps this quite old issue: #40