Add extended expression evaluator.

ExtendedExpressions/Help.txt

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+ExtendedExpressions
+
+ExtendedExpressions extends the built-in expression syntax to allow multiple
+references to a single roll within an expression, advanced bitwise, logical, and
+arithmetic operations, and more.  Expressions are evaluated internally where
+necessary, but care is taken to pass as much of each expression as possible
+along to the builtin expression evaluator in order to make inline roll tooltips
+as complete as possible.
+
+It is recommended that this script be used in conjunction with the CommandShell
+module, which will improve output formatting and command discovery.
+
+
+Commands:
+
+ExtendedExpressions adds two commands:
+
+    !exroll command
+	Acts like "/roll command", but allows extended expression syntax.
+
+    !extend command
+	Replaces expressions enclosed in backticks (`) with inline rolls using
+	the extended expression syntax.
+
+Both commands can be passed -h or --help as their only argument to get a help
+message for quick reference.
+
+
+Operators:
+
+The following operators are supported, in decreasing precedence order:
+
+    x ** y	Exponentiation
+
+    !x		Logical NOT
+    ~x		Bitwise NOT
+    -x		Negation
+
+    x * y	Multiplication
+    x / y	Division
+    x % y	Modulus
+
+    x + y	Addition
+    x - y	Subtraction
+
+    x << y	Left shift
+    x >> y	Right shift
+
+    x >= y	Comparison (greater than or equal)
+    x > y	Comparison (strictly greater than)
+    x < y	Comparison (strictly less than)
+    x <= y	Comparison (less than or equal)
+
+    x = y	Equality
+    x != y	Inequality
+
+    x & y	Bitwise AND
+
+    x ^ y	Bitwise XOR
+
+    x | y	Bitwise OR
+
+    x && y	Logical AND
+
+    x || y	Logical OR
+
+    x ? y : z	Conditional evaluation
+
+
+Additional Syntax:
+
+    "string"	String literal.  Expressions which evaluate to strings will be
+		placed inline directly rather than as inline rolls.
+
+    exp[label]	Apply label to the preceeding expression for later reference.
+		Precedence is higher than every operator except "d" (the dice
+		operator).  Use parentheses to label the size of a die rather
+		than the result of the roll (e.g. "1d(4[diesize])").
+
+    ${label}	Substitute in the value of the referenced expression.  Label can
+		be either an identifier or a string expression.
+
+
+Examples:
+
+!exroll 1t["table-number-" + 1d6] weather
+    Internally rolls 1d6, concatenates it with the string "table-number-", and
+    submits a command of the form "/roll 1t[table-number-3] weather".
+
+!extend Attack: `(1d20+7)[tohit]`, `(${tohit}>=15 ? "hit for [[1d6]]" : "miss")`
+    Internally rolls 1d20+7, compares the result against 15, and submits a
+    command like "Attack: [[12]], miss" or "Attack: [[19]], hit for [[1d6]]".
+
+!extend `1d6[foo]+1d6[bar]+${(1d2-1 ? "foo" : "bar")}`
+    Internally rolls 1d2-1, then submits a command like "[[3+1d6[bar]+3]]" or
+    "[[1d6[foo]+2+2]]".