Simplify spec helper requires

RSpec takes care of the load path for us, so this absolute path stuff
isn't necessary; but note, you still need to run these specs with
`RUBYLIB` appropriately set; ie:

  RUBYLIB=./lib:./vendor/walrat/lib bin/spec spec
Update authorship and year in copyright headers
Put license boilerplate on a diet

For similar reasons to those stated in commit
6cd8d28d57e991d2db17196f5d2ec214df85ee1c in the Command-T repo.
Update to RSpec 3.1.0

Performed the conversion with the transpec gem; ie. added it to the
Gemfile, then:

  bundle
  RUBYLIB=./lib:./vendor/walrat/lib bin/transpec -f

And then removed it from the bundle. And checked the spec suite was
still green:

  RUBYLIB=./lib:./vendor/walrat/lib bin/rspec

Here's the relevant output

  734 conversions
    from: obj.should
      to: expect(obj).to
  351 conversions
    from: == expected
      to: eq(expected)
  40 conversions
    from: lambda { }.should
      to: expect { }.to
  1 conversion
    from: =~ /pattern/
      to: match(/pattern/)
  1 conversion
    from: obj.should_not
      to: expect(obj).not_to

  1127 conversions, 0 incompletes, 0 warnings, 0 errors
Fix executable bit on library files
Unconditionally override String#each

This is ok because we're targeting a specific version of Ruby now, and
will soon switch to using refinements to keep the monkey patching
somewhat clean.

It would be nice to just use `#each_line` directly, but elsewhere we
rely on being able to call `#each` uniformly on objects that might be
arrays or strings. (Duck typing, hmph...)
Use refinements to avoid core class pollution

This is just the Walrus part; I may have to do additional work when I
make the corresponding change in Walrat.