Support the versioning system from apt

[mulino-bianco]

As apt is capable of using versions of packages, it would be great to have the same capability in colcon. Just as you could install any apt package by "apt install =", this could be defined in a corresponding rosdep.yaml and therefore here as well.

[murphm8]

Thanks for the pull request! We will take some time to review this soon.

This appears related to #118

[murphm8]

It probably makes sense to add this here, since <package name>=<version> is a valid command line argument to apt-get.

Relevant manpage quote: "A specific version of a package can be selected for installation by
following the package name with an equals (=) and the version of the package to select."

https://linux.die.net/man/8/apt-get

In the future, to support package.xml version specifiers I would probably prefer to use the metadata and consume the version information that way.

[mulino-bianco]

I agree to do this in the future. I might open another PR when I find the time.
So will you merge this one?

[murphm8]

Yes, we can merge this. I'm going to write a unit test so we can make sure this functionality doesn't break when other changes are made.

[murphm8]

Unit test added.

[samuelgundry]

Looks good, thanks for the updates.