[btcsuite/btcd] a3fa06: mining: Export block template fields. (#659)

[Dave Collins]

  Branch: refs/heads/master
  Home:   https://github.com/btcsuite/btcd
  Commit: a3fa06674512523f61a50c67a4a8f315749fcd1e
      
https://github.com/btcsuite/btcd/commit/a3fa06674512523f61a50c67a4a8f315749fcd1e
  Author: Dave Collins <d...@davec.name>
  Date:   2016-04-11 (Mon, 11 Apr 2016)

  Changed paths:
    M cpuminer.go
    M mining.go
    M rpcserver.go

  Log Message:
  -----------
  mining: Export block template fields. (#659)

This simply exports and adds some comments to the fields of the
BlockTemplate struct.

This is primarily being done as a step toward being able to separate the
mining code into its own package, but also it makes sense on its own
because code that requests new block template necessarily examines the
returned fields which implies they should be exported.