Season Update

• deparse generator expressions for Python 3.0 .. 3.2
• Python 3.0 list comprehension.
• Fix Issues #310, #344, #377, #391, #409, #414
• Limited support for 3.8+ f-string "=" specifier
• Correct 2.5-7 relative import formatting
• Miscellaneous bug fixing
• remove \n in lambda
• Python 2.6 gramar cleanup
• Correct some Python 2.6 chain compare decompilation
• Ensure no parenthesis subscript slices
• Correct 2.x formatting "slice2" nonterminal
• Correct 3.7 imports
• Improve "async for" parsing
• Handle BUILD_MAP opcode
• match Python AT better
• Correct 3.7 positional args
• PyPy 3.7 and PyPy 3.8 support
• Miscellaneous linting, isorting, blacking