Implement strong typing

[FabianVegaA]

It is required that this programming language be strong typing, for implementing the functional paradigm.

For this, you can be modified parser.py and ast.py using an Enum class, for example:

class TypeIdentifier(Enum):
INTEGER = 'int'
FLOAT = 'float'
BOOL = 'bool'
STRING = 'str'
...

Besides is required to change Identifier for implement type_value and inside have a value type TypeIdentifier