Bumping version to 1.7.3

Version 1.7.2

Version 1.7.1

Version 1.6.2

Latest production code as of 8/25/15.

Features:
MIP stability. It is now possible to set a 'MIP offset', indicating a reference point for animating inputs to makeMIP().
SparseField cache memory use reduced by reducing number of mutexes kept.
Thread safety. Re-introduced hdf5 locks in Field3DIn/OutputFileHDF5.
FieldCache keeps track of already-loaded fields and prevents unnecessary re-loading if data is still in memory.
FieldCache::memSize() tracks amount of total memory used by currently active Field3D fields.
FieldGroup now supports spatial min/max queries.
FieldGroup now supports option Add/Avg composite mode for overlapping fields.
FieldGroup now supports per-instance value remapping 'shaders' and per-instance transforms.
f3dinfo shows HDF5/Ogawa encoding
New f3dmerge app for combining .f3d files. Can also be used for converting between HDF5 and Ogawa files.

API:
coordinateSystem() version returns the extents computed.
Field3DInputFile::encoding() returns "Ogawa" or "HDF5"
Field3D::transformBounds() helper function.

Bug fixes:
discreteBounds() now prevents int overflow when converting from double.
SparseField::blockCoords now has error checking against inverted bounds and handles non-zero extents.min correctly.
MIP I/O fix to prevent concurrent HDF5 use.

Version 1.6.1

Version 1.6.0

Version 1.5.0

Version 1.4.3

Version 1.4.2