Move even more low level code into PDF::COre

Squashed commit of the following:

commit 168c44f034fa38ed4845854e6aeae400b1b64dea
Author: Gregory Brown <gregory.t.brown@gmail.com>
Date:   Mon Sep 15 15:25:26 2014 -0400

    Continue to shrink renderer's API surface

commit 0c8befe470ed79bdebc4395fbdb083120474eabc
Author: Gregory Brown <gregory.t.brown@gmail.com>
Date:   Sat Sep 13 20:53:31 2014 -0400

    Make Prawn::Document::Internals mixin smaller

commit 0071a689c39741308db092a3ddd399856e56a4ff
Author: Gregory Brown <gregory.t.brown@gmail.com>
Date:   Sat Sep 13 20:33:18 2014 -0400

    Use explicit names for delegated methods

commit a77e9aa5b81b404bbd8d3be6d36316dd2e13c6f3
Author: Gregory Brown <gregory.t.brown@gmail.com>
Date:   Sat Sep 13 20:28:30 2014 -0400

    Remove some monkey patches and push more down to PDF::Core

commit a42d70d867f8efd5fd5407dac0c3745c64cf5a1b
Author: Gregory Brown <gregory.t.brown@gmail.com>
Date:   Sat Sep 13 19:03:00 2014 -0400

    Rough integration of PDF::Core::Renderer
Use latest PDF::Core version
Use latest TTFunk version
Process soft-hyphens in blocks which do not exclude trailing white space
Back to the future
Update how_to_read_this_manual.rb
Update how_to_read_this_manual.rb
Raise an error when unsupported PNG type is found
Fix typo in text box overflow section of the manual.
Merge pull request #784 from airblade/patch-1

Fix typo in text box overflow section of the manual.
Run rubocop after unit tests
Merge branch 'master' of github.com:prawnpdf/prawn
Raise error when zero length is provided to dash
Merge remote-tracking branch 'upstream/master'