Refactoring

Added description to Ast module
Removed unused happy file
Fixed data declaration
Modified Ast, start writing parser with Parsec
Refactoring

Organized the parsers in modules
Added Boolean Expression parsers
Added Binding parsers definition
Merge branch 'master' into parsec
Added parser for Let statement and bindings
Added statement FunCall

StmBlock now requires braces {}
Added parser for For statement
Refactoring

Introduced Block module
Added "Syntactic Sugar"

No braces if statement block is just one function
Same constructor IfThenElse for construct without
else branch (used Maybe StmBlock instead).
Used more syntax to make easier the parsing

For example
  comma for let bindings
  semicolon for statements
Added some annotations for future development