Turing machine simulator

• Each line should contain one tuple of the form '<current state> <current symbol> <new symbol> <direction> <new state>'.
• You can use any number or word for <current state> and <new state>, eg. 10, a, state1. State labels are case-sensitive.
• You can use almost any character for <current symbol> and <new symbol>, or '_' to represent blank (space). Symbols are case-sensitive.
  You can't use ';', '*', or whitespace as symbols.
• <direction> should be 'l', 'r' or 's', denoting 'move left', 'move right' or 'stay in place', respectively. You can also use 'left', '<', 'right', '>', 'stay', '=', and '*'.
• '*' can be used as a wildcard in <current state> to supply default instructions for any state.
• '*' or 'else' can be used as a wildcard in <current symbol> to match any unspecified character.
• '*' or 'same' can be used in <new symbol> to mean 'no change'.
• '*' or 'same' can be used in <new state> to mean 'no change'.
• Anything after a ';' is a comment and is ignored.
• The machine halts when it reaches states named 'accept', 'reject', or any state starting with 'halt', eg. halt, halt-accept.

• '!' can be used at the end of a line to set a breakpoint, eg 'q1 a b > q2 !'. The machine will automatically pause after executing this line.
• You can specify the starting position for the head by prepending '*' in the initial input.
• Under 'Advanced options', you can specify the initial state (defaults to 'start').
• Under 'Advanced options', you can also specify whether the machine's tape is infinite only to the right (the default) or in both directions; whether the machine only accepts 'quadruple' instructions (can write a symbol or move the head, not both); and whether the machine is allowed to be non-deterministic.
• The current implementation of non-determinism is rudimentary (chooses one path at random, doesn't explore other paths).