Conda recipe linter ideas

Follow on to #42.

For the scope of this ticket, the following ideas should be implemented:
- [x] verify that package name and version are specified
- [ ] document the use of numpy *
- [x] verify that an about home and license are specified
- [x] assert that ~~an MD5~~ a checksum is defined for file sources
- [ ] assert that each patch has a comment
- [x] assert that selectors are in their "comment" form (with 2 spaces, a hash then 1 space).

To keep it concrete - any other ideas should have their own issue.