v0.7.0 - added keywords from Solidity v0.7.x and v0.8.x.

v0.6.0 - new NatSpec keywords, require Python v3.3+.

v0.5.1 - bugfix, detect `:` as punctuation in Yul.

v0.5.0 - add Yul lexer.

v0.4.1 - port back fixes from Rouge's lexer PR.

v0.4.0 - update keywords up to those in `solc` v0.6.0.

v0.3.1 - only highlight actual "nested" keywords.

v0.3.0 - highlight NatSpec specials.

v0.2.0 - update keywords up to those in `solc` v0.4.22.

v0.1.0 - update keywords up to those in `solc` v0.4.21.