* Simplify scanning of SWC records.
* `parse_swc` now retains metadata read from SWC comments.
* `parse_swc` is given two modes, relaxed and strict. Strict mode enforces contiguous record numbering and rejects SWC that looks like it has a single-point soma.
* Subtype `swc_error` according to error mode.
* Remove `point` class and corresponding unit tests.
* Add a RAII stream formatting flag saver, used in SWC record output operator.
* Replace included 1-point soma SWC example with a regular SWC from NeuroMorpho.