add example for git commit
fix example for git add
add example for git push

Implement a new example that resembles the git-stash(1) command.
Right now, it only provides the apply, list, save and pop
subcommands without any options.

This example is mostly used to test libgit2's stashing
performance on big repositories.

Implement a new example that resembles git-config(1). Right now,
this example can both read and set configuration keys, only.

Inside of our networking example code, we have a git2 executable
that acts as an entry point to all the different network
examples. As such, it is kind of the same like the normal git(1)
executable in that it simply arbitrates to the respective
subcommands.

Let's extend this approach and merge all examples into a single
standalone lg2 executable. Instead of building an executable
for all the existing examples we have, we now bundle them all
inside of the lg2 one and let them be callable via subcommands.

In the process, we can get rid of duplicated library
initialization, deinitialization and repository discovery code.
Instead of having each subcommand handle these on its own, we
simply do it inside of the single main function now.