* [control file] Add optional 'Homepage' tag
This allows a 'Homepage' tag to be added to a port in order to support
changes such as PR #2933. It currently does not do anything with it.
* [docs]
Add Homepage to the control file documentation
* move urls from descriptions to homepage field.
* add CONTROL and portfile for spectralib 0.7.0
* Rename spectralib -> spectra
I'm making this change based on the naming in the other repositories
that the library is packaged in (DPorts, FreeBSD Ports) and the
terminology used on the website. Code examples use Spectra* for the
prefixes, so I think using "Spectra" is better than "spectralib".
