Initial commit

I commit the first revision of js-calc.
Finish input and output revision

I revise and restructure the input and output handling code.

Furthermore, I add an option to configure the decimal point used in the
calculator.
Implement unary and binary operations

I implement a lot of unary and binary operations, such as plus, minus,
times, divided by, square, square root etc.
Handle calculator errors

First, I handle calculator errors by displaying an "E" and blocking all
further input except "AC".

Then, I implement the "CE" key.
Add memory

I add memory functionality and style the display indicators.
Add key press handling

I improve the usability by handling key events.
Add missing operations

I implement the missing operations y^x and x-th root of y.
Introduce further LESS variables

I introduce new LESS variables to make the stylesheets more
configurable.
Add haptic feedback

I add haptic feedback when clicking keys or pressing keys on the user's
keyboard.