* rewrite snippet parser to use different snippet open- and close
syntax. This enables support for using snippets in languages w/o
line comments, i.e. the comment spans multiple lines until
explicitly ended.
Examples are HTML ('<!-- ... -->'), CSS and classic C ('/* ... */').
The old parser would attempt submitting the remainder of the line to
the JSON parser for parsing, causing an error. Given explicit open-
and end tags, the parser will disregard anything following the close
tag.
* minor adjustments to remove warnings from mypy
* mark package as using types - this enables code consuming this library
to benefit from the type annotations.
