The notation for escapes in strings follows that of the host platforms
which is different from the notation for character literals in Clojure
(e.g., "\n" vs `\newline`).
This commit:
- Updates the keyword list with public symbols from `clojure.core` for
Clojure 1.9.
- Improves syntax highlighting of symbols, strings, character literals,
and number literals.
- Adds rules for syntax highlighting Clojure keywords and reader macro
characters.
- Fixes an issue where forms following a single semicolon (`;`) are not
marked as comments.
- Fixes an issue where parts of multi-line strings were not correctly
syntax highlighted.
- Adds additional test coverage for tokenization code.
