add optimized/separate triangle filter

This PR contains a separable optimized TriangleOptProc that address a few open issues (efficiency/speed and exceeding some platformvarying array limits). It also contains some lib/cmake refactoring to accommodate SHARED lib builds and some Windows specific fixes. The CI setup files appveyor.yml and .travis.yml are also updated to use the cleaner/simpler templates from ingenue/hunter testing as well as the drishti/bin/hunter_env.{cmd, sh} and build scripts.

add optimized/separate triangle filter

add separable optimized triangle filter TriangleOptProc + TriangleOptProcPass for compatibility with acf filtering based on GPUImageSingleComponentGaussianBlurFilter.m
- https://github.com/elucideye/acf/issues/48
- https://github.com/elucideye/acf/issues/64
add GTest for TriangleOptProc
minor gpu + acf tuning (this will always be an approximation of CPU code)
run clang-format
update appveyor/travis configs to match drishti repo -- this provide a much simpler clang linux setup without the travis permission symbolic link workarounds
be sure to wrap all OpenGL sections in #if defined(ACF_DO_GPU)

This separable filter makes use of OpenGL HW texel interpolation to replace two adjacent integer offset kernel coefficients with a single coefficient for a single (interpolated) texel lookup. The code is adapted from the following:

https://github.com/BradLarson/GPUImage/blob/master/framework/Source/GPUImageSingleComponentGaussianBlurFilter.m#L5-L186

Which is released under compatible 3-clause BSD license:

https://github.com/BradLarson/GPUImage/blob/master/License.txt

ACF lib/cmake refactoring to support SHARED builds

create acf_util from src/lib/util for internal reuse — this is allows creating a SHARED acf lib without exporting this local utils
create acf_shader from src/lib/acf/gpu for internal use -- if CMake OBJECT libraries worked portably, this would probably be an OBJECT library.
link tests and local apps with STATIC acf_util and acf_shader (optional if using GPGPU)
update RPATH handling in acf top CMakeLists.txt for relocatable install tree
simplify: use ACF_HAVE_TO_STRING result from try_compile testing directly
add ACF_EXPORT for explicit template declarations in ACFIOArchiveCereal.cpp
reduce repetition value for acf-pipeline in CI test so test finishes in reasonable amount of time
ACFField: use default destructor and fix constructor initialization order

Windows

set PATH for gauze tests on MSVC platforms
export acf::Field<...> templates
export draw() for pyramid visualization
add update ACF::updateGL() API call to support platform specific OpenGL bindings from within the SHARED lib (e.g., windows DLL + glewInit())
call updateGL() in apps/tests: acf-detector (GLDetector); acf-pipeline, test-acf

elucideye / acf