Fix enums including whitespace

[chrispahm]

The current class-based enum definition yields invalid Python syntax when enums include whitespace

class EnumWithSpaces(str, Enum):
    another value = 'another value'
    some value = 'some value'

This PR changes the output of enums using the functional API that allows us to specify the member names using tuple lists or dicts. This way we can use names with spaces:

EnumWithSpaces = Enum(
    value='EnumWithSpaces',
    names=[
        ('another value', 'another value'),
        ('some value', 'some value')
    ]
)

All tests are passing and updated to the new enum syntax.

Fixes #68