Add ability to choose a file to bump from the command line

[hmgibson23]

Sometimes it's nice just to specify which file you want change, rather than changing them all. Or at least instructions on the README on how to do this.

[mikaelbr]

Thanks for sending an issue! In what cases would it be interesting to only bump one package-file? E.g only bump version in package.json but not bower.json. Why would the version in those files differ? I don't really see the use case.

[hmgibson23]

Hi. So currently have to push to bower and npm separately as we don't want npm to automatically take the latest tags and update the version.

Another solution to this problem would be to allow for different tag formats, then we could specify how we want the tags to appear on node and bower

e.g

mversion x.x.x -m “v%s”
-m allows you to change the format of the commit
we want to be able to change the format of the tag
e.g. mversion x.x.x -m “v%s” —tag “v%s-src”

Or something to this end.

Thanks

[mikaelbr]

It still seems a bit weird to me to define package files, as this is the sort of thing I'm trying to abstract, not handling multiple files. But I can see overriding tag name being useful.

I created this PR: #13. Do you think something like this would be fine?