Change memory ordering for reference counting

This commit changes the the reference counting behavior, going
from add/sub with SEQ_CST/SEQ_CST to add/sub with
RELAXED/RELEASE+ACQUIRE.

This should make for more efficent clones and frees.

This method is inspired by the reference counter implementation in
the boost library.

https://www.boost.org/doc/libs/1_57_0/doc/html/atomic/usage_examples.html

Add custom error creator function

This commit add the tg_geom_new_error() function, which allows
for creating custom error geometries outside of the TG library.

Update API documentation

Fix segfault while serializing a geometrycollection

This commit addresses an issue where serializing a
geometrycollection may segfault.

For tg_geom_geojson(), tg_geom_wkt(), and tg_geom_wkb()

Fixes #7

Mention Webassembly and Zig

Added methods for calculating length and area.

This commit exposes the following methods:

- tg_line_length
- tg_ring_perimeter
- tg_ring_area

See #5

Ensure tg_geom_copy copies collection indexes

Updated api docs

Fix intersecting linestrings

This commit fixes an issue where fully contained linestrings are
not intersecting.

Fixes #3

First commit