Deltavision: ignore null lens IDs in the log file

See QA 4758 - 4761.
Gatan DM2: fix the pixel type for 32-bit data
Gatan DM2: ignore negative-length strings
Remove obsolete GPL license

It is now in components/bio-formats/LICENSE.txt (among other places).
Add comment about workaround for TestNG issue
Convert README to Markdown
Gatan DM2: parse more metadata from the "extra tags" section
TIFF: fix header writing for big-endian BigTIFF files

Fix suggested by Matthias Baldauf:

http://lists.openmicroscopy.org.uk/pipermail/ome-users/2012-November/003463.html
Remove unused PWD environment variable
DO not override SPHINXOPTS variable
Merge pull request #256 from ctrueden/markdown-readme-dev_4_4

Convert README to Markdown
Merge pull request #255 from ctrueden/doc-tweaks-dev_4_4

Documentation tweaks
Re-arranging user pages re ticket 7208
Actually fixing managing memory page!
Managing memory page take 3! (ah Friday)
It is fixed this time honest!
Final format and style fixing
Merge pull request #257 from melissalinkert/dm2

Gatan DM2 metadata fixes
Merge pull request #259 from sbesson/env_Makefile

Makefile
Merge pull request #245 from melissalinkert/dv-null-objectives

Deltavision: ignore null lens IDs in the log file