Complete unit tests.

[amcgregor]

• [x] Inline (single-line) constructs.
  • [x] Single-line untranslated code.
  • [x] Comments, including double-hash exclusion from the resulting stream.
  • [x] Flush. Ensure actual buffer contents are in fact flushed on demand. (And not when the buffer is assumed empty: direct buffer manipulation is frowned upon, but not impossible.)
  • [x] Text transformations. Ensure escaping happens when expected, etc.
  • [x] Inline embedding of another template.
• [x] Block (nesting scope) constructs.
  • [x] Conditionals: if, elif, and else.
  • [x] Loops, both while and for, with an optional else run-off-the-end chained block.
  • [x] Context managers.
  • [x] Exception handling.
  • [x] Template wrapping.

[amcgregor]

Completed. We now have 100% (less one line) coverage.