Typecheck predicate functions for enjoy.js

This is a collection of type checkers. It also checks for some types that only exist
in enjoy.js projects, but it's useful even for non-enjoy projects as well.

The following general type checkers are part of the module:

* isArgumentsObject(a): Checks if a is an arguments object.
* isArray(a): Checks if a is a real array.
* isArrayLike(a): Checks if a is iterable like an array, e.g. a DOMElement or Arguments.
* isBoolean(a): Checks if a is a boolean.
* isChar(a): Checks if a is a string containing only one character.
* isCollection(a): Checks if a is a collection of values (array or object).
* isDate(a): Checks if a is a Date object.
* isError(a): Checks if a is an Error object.
* isFiniteNumber(a): Checks if a is an actual number (not NaN or +/-Infinity).
* isFloat(a): Checks if a is a real number (but not an integer).
* isFunction(a): Checks if a is a function.
* isInfiniteNumber(a): Checks if a is an infinite number like NaN or Infinity.
* isInfinity(a): Checks if a is positive or negative infinity.
* isInteger(a): Checks if a is an integer.
* isMathObject(a): Checks if a is the JavaScript built-in Math object.
* isNegativeInfinity(a): Checks if a is -Infinity.
* isNull(a): Checks if a is null.
* isNumber(a): Checks if a is a number (including NaN or +/-Infinity).
* isPositiveInfinity(a): Checks if a is Infinity.
* isPrimitive(a): Checks if a is a primitive type (everything but an object/array).
* isRegExp(a): Checks if a is a regular expression object.
* isString(a): Checks if a is a string.
* isUndefined(a): Checks if a is undefined.

The module also contains these enjoy-specific type checkers:

* isDerivable(a): Checks if a is an enjoy.js derivable object.
* isMethod(a): Checks if a is an enjoy.js multimethod.
* isType(a): Checks if a is an enjoy.js type object.