Fix different location example
Adds documentation to fix #135
Remove support for Ruby 1.8.7

Ref: #193

We no longer support 1.8.7 and will no longer run the Travis test suite on 1.8.7
Add Travis support for 2.0.0

Ref #194

Let's see what happens with these tests
Merge pull request #176 from jteneycke/patch-2

Fix different location documentation example
Make middleware not executable
Option to allow caching of PDFs
Merge pull request #197 from pdfkit/jgarber-caching

[Rebased] Option to allow caching of PDFs
Don't require the wkhtmltopdf gem

It can be added/gem installed as needed. Also sort dependencies :).

One possible issue: will it need to be added to the gemfile/gemspec for
it to be picked up when running rake? Or will you be able to just `gem
install wkhtmltopdf`?
Merge remote-tracking branch 'origin/jh-fix-travis'

Conflicts:
	.travis.yml
Allow controllers to set PDFKit-save-pdf header to cause rendered pdf to be saved in the filesystem
get first PDFKit-save-pdf test passing
PDFKit-save-pdf pdf save header tests
fix merge conflict