Add BuildOption, BuildEnv and PackageOption types
Add BuildOption
which is a type to track generic option strings that
may be prefixed by a "!".
Add BuildEnv
to track option strings available to a build environment
(a wrapper around BuildOption
).
Add PackageOption
to track option strings for packages (a wrapper
around BuildOption
).
Closes #3 (closed) Closes #8 (closed)