Added Athena as output mode, refactoring & better support for '\\' strings

IMPORTANT:

In this versions there is some output changes & fixes that can break your code.

1. Now all arguments inside brackets are parsed as separate strings in the list.
   For example:
   file_format = (TYPE=JSON NULL_IF=('field') this was parsed like 'NULL_IF': "('field')",
   now it will be: 'NULL_IF': ["'field'"],

2. Added separate tokens for EQ = and IN (previously they was parsed as IDs also - for internal info, for contributors.

3. Some check statements in columns now parsed validly, also IN statements parsed as normal lists.
   So this statement include_exclude_ind CHAR(1) NOT NULL CONSTRAINT chk_metalistcombo_logicalopr
   CHECK (include_exclude_ind IN ('I', 'E')),

will produce this output:

{'check': {'constraint_name': 'chk_metalistcombo_logicalopr',
'statement': {'in_statement': {'in': ["'I'", "'E'"],
'name': 'include_exclude_ind'}}},

Fixes

1. DEFAULT word now is not arriving in key 'default' (it was before in some cases)

New Features

1. Added Athena output mode and initial support - #272