Updated the root .gitignore.

Goals:
* exclude Eclipse metadata
* don't recursively ignore target folders, as they might be used as package names
Created the jessentials-parent project.
Created the jversion-sanity project.

Has a first stab at the base interfaces and classes I think will be needed. I also included a
mostly-but-not-entirely useless IntegerVersion implementation of the API as well, to help in
validating the API.
Updated the bareint package comment to explain more about the package's intent.
Refactored IntervalMatcher for readability.

It's now using more predicate logic, which made the code simpler.