Org reader: Fix block parameter reader, relax constraints

The reader produced wrong results for block containing non-letter chars
in their parameter arguments.  This patch relaxes constraints in that it
allows block header arguments to contain any non-space character (except
for ']' for inline blocks).

Thanks to Xiao Hanyu for noticing this.
Merge pull request #1290 from tarleb/fix-header-params

Org reader: Fix block parameter reader, relax constraints
Made suitable changes to reflect changes to the Image datatype
Version bump
Added capability to read encoded images in HTML files
Added filter which writes encoded images to file so that they can be displayed in more formats
Further changes to image type
src is now read correctly
Fixed tests
Final image syntax changes
Figure changes
Modified existing figure code to work (approximately) with new figure type
Modified first 4 readers to return figure type