Introduce some uniformity into error message IDs.

All IDs should now be of the form

  CHEBFUN:CLASSNAME:methodName:errorID

or

  CHEBFUN:trunkMethod:errorID

or

  CHEBFUN:CLASSNAME:methodName:subFunction:errorID

as needed.  I may have missed a few, but this commit should get most of
these changes.
Loosen tolerance in generalized eigenvalue test.

This is needed to make this test pass on my personal machine.  (It's
fine on my departmental workstation.)
Fix URLs in copyright notices.
A few more fixes to error IDs.
Merge pull request #884 from chebfun/fix-errids

fix-errids