Make the Linux/MacOSX experience slightly more delightful

#786 brings under the light the fact that there's still a huge room for improvment regarding the following topics

• How to build libgit2
• How to run the tests against the generated binaries

Currently, all of the above is being automagically done by the build.libgit2sharp.sh script.

I can think of two options:

• Add some documentation in the script header describing what the script does, where the binaries are generated
• Break up the script into two scripts (ie. build and runtests)

There are certainly others ways to solve this.

Thoughts?

Commencez par lire build.libgit2sharp.sh et suivre la manière dont il construit libgit2, génère les binaires et exécute les tests sous Linux et macOS. Confirmez avec les maintainers si le résultat attendu est la documentation du script ou des scripts distincts de build et de test ; le travail est terminé lorsque le workflow est clairement expliqué ou proprement séparé.