Remove ECC which was set as alg 4

There is no alg 4 and ECC is not an algorithm identifier.
Merge branch 'master' of github.com:miekg/dns
SIG0 misc - doc, bounds checking, refactor tests

* expand documentation a little and tweak comments
* add bounds checking in Verify()
* refactor tests
Merge branch 'master' of github.com:miekg/dns
Fix package header
Merge branch 'andrewtj-atj-sig0'