made withIdentity() decorator more concise

If you pass something different from an APLArray, it will get wrapped in
an APLArray automatically.
added aliases for * - ∊, issue #24

New alias                       Existing symbol
---------                       ---------------
⋆ (U+22C6, STAR OPERATOR)       * (U+002A, ASTERISK)
− (U+2212, MINUS SIGN)          - (U+002D, HYPHEN-MINUS)
∈ (U+2208, ELEMENT OF)          ∊ (U+220A, SMALL ELEMENT OF)