Add a few new features to assembler

* Support ASC delimited strings to use ` in addition to '.  Using this
  new delimiter tells the assembler to set the high bit of each ASCII
  character.  This is often required with Apple II monitor calls.
* DS / shouldn't round up to next page if already sitting at the start
  of a page.  I also fixed a bug where a DS of 0 would still emit 1 byte
  because of how FOR loops work in Applesoft.
* Display final byte and error count after dumping symbols.  This way I
  can leave the machine, come back and tell whether the build was
  successful or not.
* Leave the area for the machine code reserved in HIMEM at exit so that
  Applesoft BASIC won't touch it after assembly has completed.
* Added test cases to cover these new features when possible.
* Updated ASC documentation in features.creole to cover the new
  delimiter option.
My first Applesoft utility in assembly language

Yesterday I wrote DSPACE in 6502 assembly language using my simple
BASIC based assembler.  This utility walks a tokenized Applesoft
BASIC program in memory to find and removes leading spaces in DATA
statements.

As I edit lines like this in my assembler, I end up getting more and
more spaces inserted between the DATA keyword and the opening quote
because of how LIST outputs the DATA token and how the cursor scan
editing feature works.
32000 DATA    "; KEEP GETTING SPACES BEFORE THE QUOTE"

If I forgot to skip the spaces between DATA and " during an edit scan
then yet another space would get added.  They get skipped during READ
but they take up space in the code and just make it look ugly when
LISTed.