some additional features / convenience funcs

[AndreasBriese]

Hi,
i added _.sum() _.mean() _.median() to collections section and nrange() to arrays. tests are adjusted appropriately.
in further detail:
_.sum(obj): returns the sum of the elements objects.
_.mean(obj): returns the mean of the elements in the object.
_.median(obj): returns the median element (middle in sorted). works also with string / char elements (i.e. to split lists of names by alphabet)
_.nrange(n) adds convenience functions to _.range(n):
nrange(-3) -> [0, -1, -2];
nrange(0,3) -> [0, 1, 2];
nrnage(3,0) -> [3, 2, 1];
(might replace _.range(n) to reduce redundance)
do{}while() instead of while(){} speeds up the script slightly on FF4+ and Safari.

test suite and speed test is adjusted and tests passed.

Andreas

[jashkenas]

Lovely stuff, but I'm afraid that it's a bit out of scope for core Underscore.js functions. I'd love it if you could wrap it up as an _.mixin plugin, and add a link in the Wiki.