Add Developer Examples; Transaction Tutorial

* Add new Developer Examples page

* Add a transaction tutorial describing in detail how to make various
  different transactions.

* Add a new "multicode" CSS class to allow combination of consecutive
  code blocks into a single code block. This lets us use pygments
  highlighting for multiple different types of code within the same
  aparent block of code.

* Get autocrossref to ignore code blocks so we don't need to endcrossref
  every time we encounter a code block. This makes the source much more
  readable and maintainable.
Move BIP70 Example To Dev Examples

* Move the extened BIP70 example from the guide to the developer
  examples page.

* Add new text introducing BIP70 to the guide
Add Icons; Update Links

* Add new icons for Developer Guide and Developer Examples so we don't
  keep reusing the book icon.

* Update payment protocol links to point to developer examples when
  appropriate.
Merge remote-tracking branch 'bitcoin.org/master' into generatingtxes

Conflicts:
	_includes/guide_payment_processing.md
	_less/screen.less
Add Disclaimer & Anchor Affordance To Dev Examples
Updates Based On Feedback From Mailing List

* Remove the QR Code error corrections subsection.

* Remove the non-example Payment Protocol text from developer examples.

* Update reference links and autocrossrefs to reflect above deletions

* Fix CSS padding problems reported by @saivann

* Remove all HTML comments from autocrossref text to allow easy checking
  for broken link definitions: find _site -name '*.html' | xargs grep '\]\['

* Add PNG versions of guide and example SVG icons.  (optipng run)
Add Report Issue Link To Developer Examples
Use consistent capitalization for devel-doc icons
Fix "Return To Overview" icon in devel-example
Apply consistent width and center icons in devel-doc
Simplify multicode CSS styles
Add consistent border-radius
Simplify margins / paddings
Merge remote-tracking branch 'saivann/generatingtxesmulticode' into generatingtxes
Use consistent names for 48px icons
Add Tx Malleability Warning To Spending Unconfirmed Tx Example

Suggested and written by @saivann, with a revised version being
commited here. Thanks!
Add Note About Tx Fees To All Createrawtransaction Example Calls

Based on feedback from @saivann, this may help remind users that poor
use of createrawtransactions can cost them satoshis.
Move Gavin's Payment Request Generator to the "Examples" page
Fix various typos or naming inconsistencies
Add BIP71 and BIP72 to autocrossref links
Merge remote-tracking branches 'saivann/generatingtxesbips', 'saivann/generatingtxesresource' and 'saivann/generatingtxestypos' into generatingtxes
Clarification Of PaymentRequestss And Payment Verification

* Clarify a few places where payment request was used instead of
  PaymentRequest.

* Clarify that payment isn't necessarily verified until the merchant
  says so. Suggested by @saivann (thanks!)