* 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".
