Log Message:
lowdown: update to 0.8.0.

ChangeLog:

Version 0.8.0, 2021-01-31

Recognise the volume, source, and section metadata. These are currently
only used by -Tman.

Convert all internal functions to return an error code on memory allocation
failure. Prior to this, these functions had a chance of exiting and
printing failure to stderr. Now, this is left as the responsibility of
the front-end. There's no significant API change except that all renderers
return a value.

Fix the difference engine in several subtle ways, improving the produced
scripts, and also fix crashes where similar text would match multiple
parts of the parse tree, resulting in assertions.

Re-write the -Tms and -Tman generator to use a completely different
internal algorithm. This algorithm, instead of formatting directly into
output, converts the AST into an array of output blocks marked either as
text, literal, macro, or font/colour change. An assembler for this array
manages newlines and spacing between blocks. This fixes all known instances
of unexpected line breaks and allows for significantly simplified handling
of text interspersed with macros (e.g., links, etc.). An API result of
this is that the tree passed to lowdown_nroff_rndr(3) is now const.

Recognise non-block and block lists for -Tlatex output.

Emit a UTF-8 preconv header to all -Tms and -Tman so that -Kutf8 need not
be passed to the formatter.

Remove the --nroff-hardwrap option, which needlessly complicates code
without benefit.