New features for commands and actions

[jabraham17]

general

• cli flag to treat ebreak as PAUSE, otherwise noop
  • this is shorthand for pause if $m[$pc] == ebreak on hart:after_execute
• add shorthand cli flag --start-paused and -p
• add a single-step command
• new set command to set expressions
  • will set lhs = rhs
  • rhs can be any expression
  • lhs must resolve to a register (or PC) or a memory location
• unify PC to be defined as a register
  • Generalize PC expressions #70

context

• default events based on if CLI or interactive
• execution modes
  • if there are events defined, install as a callback
  • if there are no events defined, execute immediately
• enforce certain commands trying to execute immediately that cannot, i.e. from CLI, this is an error

new syntax

• add string support
  • Add parser support for strings #55
• dump, arg1,arg2,...
  • prints args on a single line, space-separated
  • will support other modifiers
  • Add parser operator to do multiple things #54
• modifiers like /x for hex, /u for unsigned, /ns for no space
  • hex printing from ishell #51
• action lists and event lists are semicolon separated
• watch command is now defined as watch expr,action1,action2,...
  • actions on watch trigger are passed as var args
  • Generalize WATCH #45
• allow reference to ELF symbols with @

bugs

• Parser does not recognize proper precedence #57

future

• consider adding global variables
  • something like create arg or define arg
  • then it can be used anywhere
• add a start and stop event
  • in combination with variables, we could now have statistics at runtime
• consider support for loops? probably dont want
• .. spread operator to support ranges
• print ranges of values such as $x0..$x12 or $m[0x989..0x9900]
• Add ability to remove commands #61