Ignoring out.pir file
New syntax

Now `->` replaces `=`. I think it's much pleasent to the eyes.
Add expression in «else clause»
Add modulo operator %

Also function's name are now protect with a pair of ' in PIR code.
Fix bug 'number in function name'

Now function names could be named like "foo2".
Add some tests for function naming
Reorganize fixture files
Say what is a word
Improve AST display
New syntax: ";" is an alias of "else"
Update readme