Added errors for unimplemented features

[Tsygankov-Slava]

Fixed catch location detection.

Added errors for unimplemented features and tests:

• finally syntax
• readonly classes syntax
• first class callable syntax
• intersection types
• explicit octal integer literal notation
• constants in traits
• standalone true type
• catching multiple exception types
• true type
• iterable pseudo-type
• links in list()
• yield & yield from

[mkornaukhov]

I cannot find any test on octal numbers