`<br>` is not a block-level html element
Take out the block-level html test for (non-block) `<br>` tag
Add a testcase for reported defects (and the desired output)
Split CFLAGS into CFLAGS & LFLAGS (clang whines about -L when not linking.)
add a dummy cast to the two `sort_by_`... functions to make clang and gcc
shut the fuck up about pointer type mismatches.
Add $LFLAGS to the build line for theme
don't forget to include `tags.h`
Tweak the configure process to

1. Report back which broken compiler was detected (IS_GCC or IS_CLANG)
2. If the offending compiler is gcc or clang, add appropriate -Wno-
   flags to make it stfu about constructs that Big Brother disapproves
   of.
3. emit the substitutions for CC and CFLAGS during AC_OUTPUT instead
   of during C compiler detection (this means that if you don't check
   for a C compiler, CC and CFLAGS will get set to the empty string
   in substituted files!)
Rework the internals of CLIP() so that it always assigns something to S(t);
this makes anal-compulsive C compilers (I'm looking at _you_, clang) stop
whining about unused values in expressions.
I don't need to turn off unused value warnings in clang now that I've reworked CLIP()
I macro if(e) into if( (e) ) if gcc or clang are detected
Be paranoid; check to see if S(t->text) before looking at T(t->text)
Tweaks to argument handling
Modify the search order for shared library detection (macOS weirdness)
strip out the (orphan?  does not affect the test suite) code that calls `linkyformat()` with a NULL ref
Modify `theme` so that I can pass in options (with -C & -c; -o is used)
Use `|` instead of `<` & `>` to force start of word/end of word alignment
for smartypants substitutions.
Add support for github flavoured markdown linebreaks (by adding new
functions that pad every input line with two spaces.)
Create the `gfm_string()` method that does github flavoured markdown
on strings.
Add prototypes for the two gfm_...() input methods