Standalone refactor

[wynro]

Mainly, moved a lot of the functionality that was previously inside he the ipcalc function to a bunch of separated functions, to allow independent usage, and (I think) cleaner code.

Also added the functionality to insert the report in the current buffer using the universal argument (Now, by doing C-u M-x ipcalc RET 192.168.25.0/24 RET the full report is inserted on the current point).

I have also added a bunch of tests to ensure that I didn't break anything during the refactoring.

There are still a couple of rough edges (for example, if you try to calculate the min/max host of a very small network, like a /31 or /32, it gives nonsensical answer), but I think this is good enough

You commented about bumping up the version. If you don't mind, I would prefer you to review this and then bump the version once we agree this is prepared to be merged.