Fix undefined behavior from sequence point rule violations.

Code that looks like

    *dest++ = do_something_with(*dest, ...)

results in defined behavior.  This triggers a warning when using
-Wsequence-point on GCC (which is enabled by -Wall).

Replace any such usages with:

    *dest = do_something_with(*dest, ...);
    dest++;
Fixups for GCC's unused variable warning.

- BandPassTransform::BandPassTransform(): delete unused variable z2
- Documentation.cpp: print value of response
SIMD optimization
Fixed compilation error on g++ < 4.8 (bug http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51033)
Fixed https://github.com/vinniefalco/DSPFilters/issues/15

Pointer arithmetic unspecified behaviour in Cascade.h
Fixed SSE filtering
Merge branch 'unused-var-warnings' of https://github.com/mbolivar/DSPFilters
Merge branch 'sequence-point-errors' of https://github.com/mbolivar/DSPFilters