Implement breakpoint capability

[duncanamps]

Basic at this stage. Need the concept of a permanent breakpoint which has been set by the user, and a temporary breakpoint which is set by the system. Temporary would be used, for example, with step over command by setting a temporary breakpoint after the current instruction.

• Introduce breakpoint array with permanent and temporary breakpoints
• Amend execution module to test for, and handle the breakpoints

Later development will be to set up the step over command, this is dealt with on issue #5