bump versions in non-json files

[geddski]

Might be nice to support this, in the cases where you have comments in source files that contain the version number.

[sholladay]

Just stating the obvious here. It is easy to bump the version number in package.json (etc.) because it describes a state. Version numbers in other source code forms often represent points in time.

For example, I recently made a tool to automatically bump versions in my README.md files. As soon as I needed to say something in the README.md like "This feature works since version 1.2.0", it fell apart because that instance must never be changed. I didn't want to insert some kind of custom annotation garbage just to tell my tool that. So I fell back to using a convention of only bumping the first match of a simple regex that looks for something like **Version:** followed by a semver sequence. That works well but it's special and limited.

In sum, I support this, but it should be configurable and off by default.