Add information to retrieve complete file history

A commit changed the location of source files. Unfortunately, github interface doesn't show the history past this change. Added a documentation based in a stackoverflow post about how to access this history.
Fix 's' value mapped to the 'a' byte

In `ASCIIBytes.cs` the value for 's' is incorrectly mapped to the byte
value of 'a'.  This patch corrects the issue.
Merge pull request #269 from kppullin/ascii-bytes-s-character-fix

Fix 's' value mapped to the 'a' byte
Add execute bit on NuGet.exe

For Linux / Cygwin
Added 2 elementary speed tests
Async first attempt