Generate pointer types correctly

[amirgon]

I just realized a few things:

• Pointer types are not generated correctly.
  Example:

from pycparser import c_parser, c_ast, c_generator
parser = c_parser.CParser()
gen = c_generator.CGenerator()
ast = parser.parse('const int ** const  x;')

>>> gen.visit(ast.ext[0])
'const int ** const x'
>>> gen.visit(ast.ext[0].type)
'const int'
>>> gen.visit(ast.ext[0].type.type)
'const int'
>>> gen.visit(ast.ext[0].type.type.type)
'const int'
>>> 

In this PR I fixed it and now it makes more sense:

>>> gen.visit(ast.ext[0])
'const int ** const x'
>>> gen.visit(ast.ext[0].type)
'const int ** const'
>>> gen.visit(ast.ext[0].type.type)
'const int *'
>>> gen.visit(ast.ext[0].type.type.type)
'const int'

• There is code duplication between visit_ArrayDecl/visit_TypeDecl and _generate_type. In order to use _generate_type, all that is needed is to prevent it from emitting the declname when we only want to generate these decls.
  In this PR I removed this code duplication.

[eliben]

Thanks for the fix! Just one minor nit

[eliben]

Please have a space after the comma in argument lists. Wrap the second argument if it doesn't fit in 80 lines (see examples elsewhere)

[amirgon]

Personally I think that the strict 80 character limitation is archaic and irrelevant with today's display sizes.
Anyway... Fixed on 878527b.