[ fix-agda-whithespace ] Added .agda, .cabal and .md files.

In test/succeed/LineEndings/ we test that Agda can handle various
kinds of whitespace (pointed out by Nils), so we exclude this
directory.
Merge branch 'fix-agda-whitespace'
Fixed whitespace issues.
[ HACKING ] Updated documentation related to fix-agda-whitespace.
Merge branch 'maint-2.4.0'