Renamed Variable to MemoryInteger; replaced the Variable class with a simple shell class that can hold a Register or one of the MemoryInteger types.
Documentation: updated to unify Variables and Registers
Updated the docs to reflect the fact that the disassembly now works for all architectures.
Fixed the known issue about PIC18 stack traces.  One slight problem still left is that for 2-word CALL instructions, the address in the stack trace will not be the address of the CALL instruction but it will be the address of the NOP instruction in the second half of the CALL.  I think that is acceptable.
Variable: Removed the inspect method because it was concealing the underlying type of the object.
Removed Sim#sfr, Sim#nmmr, and Sim#sfr_or_nmmr.  Renamed Sim#register to Sim#reg, which is the substitute for all the methods that have been removed.
sim.rb: Minor reordering of the 'require_relative' calls at the top.
Fixed a few problems in Variables.md.  The method is now named reg instead of register and it returns a Variable object.
Improved the comment for the Memory class.
docs: Got rid of three links to the non-existent file 'Registers.md'.
Merged in the dev/paul/storage branch.  This renames the Variable class and its subclasses to names based on RPicSim::Storage::MemoryInteger.  It removes the three ways of accessing special registers (#sfr, #nmmr, #sfr_or_nmmr) and replaces them with one way, the #reg method.  It wraps all variables and registers in a new class called Variable in order to limit the number of classes the user has direct access to.
Running.md: Phrased a sentence in a nicer way.  Instead of 'you will need to be able to' it is now 'you can'.
Variables.md: Fixed some capitalization in section titles.
MemoryWatcher: Removed the code that attempts to know all of the SFRs that might spuriously change on the first step of the simulation.  To use MemoryWatcher properly, you should arrange for the first step to be something harmless like a GOTO, and after taking the first step you should clear the MemoryWatcher with the #clear method.  There are too many registers that could be modified on the first step for the different devices to make it reasonable to catch them all.