Changed regex Prism.languages.javascript.number

Regex treated var names matching /[a-f]+/ as numbers.
Added support for scientific notation (e.g. 1.23e-4).
Added support for upper case notation (e.g. 0xBEEF).
Trimmed empty lines (sorry for the mess).

Small issues remaining:
* Leading decimal point is marked up as 'punctuation', instead as part of the
number (e.g. .1; 0.1 is matched correctly). Maybe a problem with the
tokenizer?
* Maybe Prism.languages.clike.number should be changed as well?