Infer the reader driver, no options required

This patch adds a StageFactory::inferReaderDriver() method that takes
only a filename, no options. The provided options were not used as part
of the inference process, so the base method should not required them.
The original inferReaderDriver(std::string, Options) has been updated to
call this new method.
Without reader type, infer from filename

Add logic in PipelineReader::parseElement_Reader to attempt to infer the
reader type from a filename provided in the options, in absence of a
explicit type.

Fixes #278.
a more straightforward way of setting the nitf writer options
Add icebridge reader.
Merge remote-tracking branch 'upstream/master' into hdf5
Updates for changes concurrent with this branch.
Merge branch 'master' into issue/278-infer-reader-type

Conflicts:
	src/StageFactory.cpp
Added an HDF5 include guard around an icebridge include.
Remove todo
Merge pull request #336 from gadomski/issue/278-infer-reader-type

In a pipeline, infer the reader type from filename in the absence of a type attr
Improve the las reader's file signature error

Catch the las header's invalid file signature error and improve the
error message, mostly by including the file name. In order to provide
the filename under more circumstances, set the "filename" option when
using the filename-only las::Reader constructor.

Fixes #277.
Merge pull request #351 from gadomski/issue/277-inval-file-sig

Improve the las reader's file signature error
Merge pull request #348 from chambbj/issues/346-nitf-error

A more straightforward way of setting the nitf writer options.
Merge pull request #350 from connormanning/hdf5

Add HDF5 support and Icebridge Reader