Фотьев Василий 2538

There are 2 text views, one is for input expression and the other is for result number. If you click on the result number and the input is empty or ends with either +,-,*,/ or (, the result number is appended to input.

Known bugs:
* Arithmetic is handled by IEEE 754, e.g. 1/0=+inf, -1/0=-inf, 0/0=NaN
* There is no button for infinity, however parser handles it as a number
* On orientation change result textView is cleared