Adding external PR guidance to CONTRIBUTING.md
Merge pull request #1363 from rleigh-dundee/cpp-tiff-pixeldata4

C++: Add TIFF strip/tile write support
Merge pull request #1364 from hflynn/external-prs

Adding external PR guidance to CONTRIBUTING.md
cpp: Adapt to Boost 1.56 optional changes

- Explictly dereference optional values
- Use double negative for comparing to true
Merge pull request #1370 from rleigh-dundee/cpp-optional-fix

cpp: Adapt to Boost 1.56 optional changes
cpp: VariantPixelBuffer explicitly includes type_traits
start of parameterised pixel tests
cpp: tiff: Factor out tile flushing from IFD WriteVisitor operator
cpp: test: PixelTypeConversionVisitor fixes
cpp: test: tiff uses unsigned constants
cpp: tiff: Parameterise all TIFF write tests
wip
wip
fix
fix
fixread
fix