grammar: added if without braces

It is now possible to use the simple construct
if (true) x = 2; else x = 3;
git: remove Parser.output, it has nothing to do there. Add Eclipse files to facilitate build.
grammar: Remove useless non-terminal nvar

nvar is a duplicate of the terminal NVAR, and does nothing to help
grammar: Improve error reporting for syntax errors

Add message to SyntaxErrorException.
Up to now, even if the constructor allowed a message, it was not taken in account.
grammar: Fixed the decrement postfix

If the decrement sign was attached to a variable, it was included in the name, confusing the parser.
grammar: Fixed empty Strings

Default contructor created a wrong instance of string constant, leading it to be unconsistent in the output.
grammar: Fix for (string)

String between parenthesis were not recognized, so the grammar could not read back what it output.
grammar: regen
tests: Completed grammar syntax test suite
tests: Improve error reporting in tests
.gitignore: Add *.amh script files