Merge: projects: update some short descriptions

Improve (or create) the short description of some random projects.

Note that using the fist line of the `README.md` is maybe not the best approach since the first line of a README is often a short title (approx 30 chars) whereas, to be informative the short description (synopsis) is often a long title (approx 70 chars).

Pull-Request: #1670
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>

diff --combined lib/core/README.md
index cd780d0,7833f37..7833f37
--- 1/lib/core/README.md
--- 2/lib/standard/README.md
+++ b/lib/core/README.md
@@@ -1,4 -1,4 +1,4 @@@
- # Nit Core Library
+ # Nit common library of core classes and methods
  
  Core classes and methods used by default by Nit programs and libraries.