Development version 3.43d - minor enhancement

(1) Use the "safe print" routine to avoid an additional error while trying
to print a line during exception handling.
Initial implementation of .h4, .h5, .h6 directives
Rework of .h"n" code for code consistency
Merge branch 'develop' into h456
Merge branch 'master' of https://github.com/wf49670/ppgen.git into develop
3.44a: Fix errors handling multipe small-cap strings on a single line
Merge branch 'develop' into h456
Merge branch 'develop' of https://github.com/wf49670/ppgen.git into h456
3.44b: support for .h4/5/6

Also: ppgen will now warn if the file (fn=) specified on a .il command
does not exist in the images directory. Previously it checked only the
file specified on the link= operand of the .il command.
3.44c: Implementation of .cm directive for multi-line text captions
Better handling of wrapping for long caption lines in text output
Another fix for sc handling:
(a) missed a reg-ex ? to make a match non-greedy
(b) need to restore protected characters before checking if sc string is
upper- or mixed-case.
Merge branch 'develop' of https://github.com/wf49670/ppgen into develop
Bump version to 3.44d
3.44e: Allow PPer-supplied link text to contain markup (italic, etc.)
This allows a PPer to specify something like: #131<i>a</i>:il131a# which
previously failed parsing and just left the entire string in the HTML output
3.45: Move Development 3.44e into production