Merge pull request #5 from sebastian-c/master

Option to not produce images
Updates to metadata extraction code.  Updated manuals.
Minor updates

Update to read.asd() to change in.file.ext to spec.file.ext

Updates to spec.utils:extract.metadata.se() function
update to .gitignore
Updates to extract.metadata.se.  Added .Rbuildignore
Updates to extract.metadata.se.  Added .Rbuildignore
minor updates.  updated manuals
minor updates