Updating gitignore for some local files
Ok, we have three generators (parisi, well and isaac) (^_^)
Separated the TODO list from the Readme so it can be
read and extended easily
Edited the changelog with some information about
today's experiments.

The experiment has been to change the pr_rand() function
to a pr_calc() function and a define that wraps a
reference to the wheel of random numbers from
pr_default_state if the index is not 0 or a call to pr_calc
and then a reference to the whell. Just as it is done
for ISAAC.

The results show that almost none improvement in speed
are achieved, so the code is left as is. Also, changing
the function to a define will surely break something.
So it's best left as it is now (^_^)
Added the Xorshift generator

I have added the same generator that Marsaglia has in
his paper but I haven't been able to find where the ***
he obtain the numbers 11, 19 and 8 from as they are
nowhere else in the original paper...

Also, important note: This generator does not produce
the number 0.
Merge branch 'xorshift' into devel
Added stdlib's random number generator to the speed test
Merge branch 'devel'