Fixes issue #1.

- Direct addresses can only be encoded in a short form ("FastDirect") if
  the address context is A (the second argument of binary instruction or
  the argument of a unary instruction.)
Fixes #2.
[Pulsar] Switched location and words in assembly listings.
[Pulsar] Fixed import formatting.
[Nebula] Finished first draft of the user's manual.
[Pulsar] Support for the ABT instruction extension.

- ABT ("abort") causes the DCPU16 to stop execution instructions or
  handle interrupts and enter a low-power state. In essence, it shuts
  the processor down.
[Nebula] Changed the message for an aborted DCPU16.
[Nebula] User manual corrections.
Merge branch 'master' of github.com:hakuch/Dcpu16Universe