New Streams

* Multiple filters per stream
* It's now possible to append data to compressed streams
* Stream compression is reentrant (multiple calls to `compress!` will have
  stream deflated only once).
* A few additional filters from PDF spec
  * ASCIIHex
  * ASCII85
* DCT filter is a stub as it's used only in JPEG images. It doesn't
  decode/encode JPEG images.
Fixed Stream on Ruby 1.8
Removed unused filters

Threre probably should be a gem with all the filters that are not used in
the core.
Typo fix (thanks shanepinnell)

Fixes #453.
Foreword. Closes #275
Copyedits
Typo fix
Fix table cells to allow different variants of the same font

Fixes #455.
Explicitly set row on dummy cells [closes #452]
Merge branch 'second-page-header-fix'
Delegate background_color to the master_cell [closes #412]
Probably don't need Forwardable for just this
Switch to SSL Rubygems source
Merge branch 'streams' of git://github.com/cheba/prawn
Fixed typo in code (prawnpdf/prawn#464)
Merge pull request #465 from cheba/bug-464

Fixed typo in code (prawnpdf/prawn#464)
update this spec to use the pdf-reader 1.0 API

* The pdf-reader API from < 1.0 is deprecated
depend on pdf-reader 1.x and pdf-inspector 1.1

* to use the pdf-reader page based API (introduced in 1.0)
* the pre 1.0 API to pdf-reader is deprecated and will be removed
  soonish
Replace rails.png for indexed-color test

We do not have the rights to distribute rails.png, so this commit
replaces it with a free variant. The image we are using,
data/images/indexed_color.png, was retrieved from:

http://en.wikipedia.org/wiki/File:Adaptative_8bits_palette_sample_image.png

and according to that page is in the public domain.

Closes #481.
checking graphic_state of previous page exists before duping while creating new page