ast literals

A better way to construct ast nodes than using constructor calls.

Instead of saying:

mie = MethodInvocationExpression(ReferenceExpression('print'), StringLiteralExpression('Hello, world'))

ast literals allow you to say:

mie = ast

or:
mie = ast:
print('Hello, world')

In other words, you can construct ast objects directly from boo code.

Expression, statements, blocks and type members are supported.

A next step would be ast interpolation.