Replace deprecated driver_output_term with erl_drv_output_term

Signed-off-by: Peter Lemenkov <lemenkov@gmail.com>
more sophisticated implementation, naming and unit tests

perl:eval(Code)
    evaluates arbitrary perl code and returns value

perl:define(SubCode)
    expects an anonymous subroutine definition. such subroutine will be
    compiled and installed in a namespace. Returns a name that represents
    installed subroutine

perl:call_sub(SubName [, Args]) invoces previously installed subroutine
with provided arguments. Returns return value of the subroutine.
removed js-related source files
bits of documentation in README