Commas

Lex `,` as `COMMA`.
Closing Bracket

Lex `]` as `CLOSING_BRACKET`.
Opening Bracket

Lex `[` as `OPENING_BRACKET`.
Empty list

Parse `OPENING_BRACKET EOL* CLOSING_BRACKET` as `list`.  This only
supports empty lists as a minimum viable list.
Keyword list with emptyParentheses values

Break `keywordIdentifer` into `keywordKey` for the portion before
`COLON`.  `keywordPair` combined `keywordKey COLON keywordValue`.  Zero
or more `keywordPair` can exist in a `list` to form a Keyword List.
Allow EOLs after COLON in keywordPair

Newlines are allowed after the `COLON`, but not before it because the
`keywordValue` and `COLON` must be next to each other to match
`keyword_identifier` in elixir_lexer.erl.
Split invalid test case from valid test cases
OPERATOR_KEYWORD -> KEYWORD_KEY_LITERAL

`KEYWORD_KEY_LITERAL` will be used for more than just operators as there
is a bug that spaces are allowed between ALIAS, IDENTIFIER, and quote
and the COLON in keywordPairs when that isn't allowed by
elixir_lexer.erl.
Disallow space between ALIAS and COLON in keywordPair

Lex `{ALIAS} / {COLON}{SPACE}` as `KEYWORD_KEY_LITERAL` and remove
`ALIAS` from `keywordKey` so that only Aliases that are immediately
adjacent to ": " are allowed as keyword keys.
Disallow space between IDENTIFIER and COLON in keywordPair

Lex `{IDENTIFIER} / {COLON}{SPACE}` as `KEYWORD_KEY_LITERAL` and remove
`IDENTIFIER` from `keywordKey` so that only Identifiers that are immediately
adjacent to ": " are allowed as keyword keys.
Disallow <quote><space><colon>

When encountering a `QUOTE_PROMOTER` (`"` ir `'`) put the return state as
`KEYWORD_PAIR_MAYBE` instead of the current state.  The
`KEYWORD_PAIR_MAYBE` state checked for `{COLON} / {SPACE}`.  If it is
found, it is lexed as `KEYWORD_PAIR_COLON` and the lexer returns to the
state where `QUOTE_PROMOTER` was detected. If `{COLON} / {SPACE}` is not found,
then the token is handled in the state where `QUOTE_PROMOTER` was detected.
Pass all potential keywordKeys through KEYWORD_PAIR_MAYBE

Instead of detecting keywordKeys for operators, ALIASes, and IDENTIFIERs
using the `/ {COLON}{SPACE}` trailing syntax and lexing them as
`KEYWORD_KEY_LITERAL` followed by `COLON`, have all operators, `ALIAS`,
and `IDENTIFIER` go the the `KEYWORD_PAIR_MAYBE` state, which will parse
`{COLON} / {SPACE}` as `KEYWORD_PAIR_COLON` that was used with `quote`.
This leaves the `COLON` token type available to be parsed for a
correctable error when there is a space between the `ALIAS`,
`IDENTIFIER`, operator, or `quote` and the `COLON`.
Add Keyword Lists to README
Lands #56, Keyword Lists
Update changelogs