Dev Docs: Detail Transaction Format

Provides a detailed description of the transaction format, replacing an
example hexdump taken from the wiki.

I'm putting this in the transaction section as the format is necessary
for the creation of txids, which are used as merkle leaves (so are
covered by consensus rules).  However, this is also the format used by
several P2P network messages to transmit transactions, so I'll be
linking back to it from there as I document those messages.
Change Text Alignment & Fix Some Typos

* Replaced text justification with left-align (raggedright) for all text
  in dev docs.

    * Removed previous manual left-align in RPC byte order table

* Changed placement of See Below text partly based on a suggestion by
  @saivann (thanks!)

* Normalized capitialization of special structures (e.g. s/TxIn/txIn/)
  to be consistent with some other parts of the docs. (I don't think
  we're fully consistent on this in all parts of the docs. I'll put a
  rule in the style guide today and then we can make changes on the next
  global proofread.)

* Fixed missing period found by @saivann (thanks!) and a related missing
  preposition.
Merge branch 'tx-format' (pull #631)