Fix: End of JavaScript comments are not parsed

[anseki]

Issue:
#77 (comment)

In JavaScript code, that regexp stops reading immediately it found * without checking */ or end of line, etc..
Because that regexp accepts these as the end of the directive:

1. **
2. */
3. Nothing

That regexp accepts "Nothing". And * as the parameters is not accepted.

For example:

console.log(
  require('preprocess').preprocess(
    'foo/* @if SIZE * 1024 > MEM */ BIG/* @endif */ bar',
    {SIZE: 2, MEM: 1024},
    {type: 'js'}
  )
);

Result:

foo* 1024 > MEM */ BIG bar

This PR fixes this bug, and puts common patterns into the variables.

[anseki]

I renamed vars because those are not good naming.
If I should do it, I do rebase to a one commit.