Add strike-through support in ODF output
Add strike-through support in LaTeX output
Add strike-through support for groff output

A groff macro is defined to strike through words enclosed in pairs of
`~~` when rendering to the Postscript device. The macro doesn't yield
suitable results when rendering to any device other than Postscript.

As the macro application requires that the string be placed on its own
line, leading dots have to be escaped that result from splitting strings
like `~~Hello~~. Goodbye` after the last `~~`. Without escaping, the
groff output would be

    .ST "Hello"
    . Goodbye

leading to a failure to process ". Goodbye".
Merge upstream branch 'master' into strike-extension
Rewrote Strike parser to avoid exponential blowup.
Merge pull request #20 from rekado/upgrade-peg

Upgrade from peg 0.1.4 to peg 0.1.9
Removed unneeded peg-memory-fix.patch.
Fix makefile to build peg, remove peg-exe-ext.patch
Refactoring to build on windows

all .c files now build as separate files.
code has been refactored to not depend on inclusion of .c files
functions in utility_functions.c are now extern
removed strdup and strcasecmp prototypes, now use .h files
fixed inconsistent linkages in markdown_output.c
Fixed distclean so it doesn't wipe out peg directory.
Removed optimization flag that requires newer GCC.
Only obfuscate ascii characters.

See fletcher/peg-multimarkdown/issues/139 for background.
Treat <head> as block-level HTML tag.

Closes #21.
Merge branch 'upstream'
Merge remote-tracking branch 'origin/strike-extension'