Changed inclusion order according to project custom.

We usually include QuantLib headers first, then Boost ones, then those
from the standard library. This is to make sure that macros are properly
defined before including other stuff.
Moved FFT and autocovariance implementations into core library.
Enforce self-consistency of headers.

Headers should compile even when included alone.
Merged branch heads.
Updated list of copyright holders.

Also, a few copyright attributions were cleaned up of typos
and alternative spellings.
Replaced hard tabs with spaces.