README.md: update builddir setup command
docs: fix/update
README.md: specify implemented version
Update collections API/logic
Rewrite everything /o\
snconv: update, allow plus signs
Update/unify the semantics of scalars

This ensures the meaning of scalars is 1) consistent and 2) doesn't
depend on their types.
snconv: fix typos
tests: add bad character test
scalar: use memcmp() for null/bool
Update multiline scalar explicit end semantics
scanner: fix get_indented()
tests: print error description
Clarify that string length is in octets
Use "collection" instead of "vector"
Add error descriptions
Avoid lines longer than 80 characters

This doesn't apply to data in snconv.c.
meson: rename dependency variable
Improve scalar type logic
docs: remove outdated info