Import previous work

Note that 'Makefile', 'timer.h', and 'utils.h' are derived from
https://github.com/udacity/cs344 (license unspecified).
Refactor pyramid class
Add output routine
Add DR compression routine
Implement slow local Laplacian filtering
Build with debugging symbols
Implement fast local Laplacian filtering
Fix typo in formula used by fast filter
Fix bug in remap kernel
Fix another bug in remap routine

Also add pyramid mixing code.
Tweak parameters
Add color (Y-channel) filtering
Generalize Makefile

Use variables for C++ compiler and CUDA architecture, along with other
minor changes.