Rework risugen's parser to use Text::Balanced rather than split.
Rework risugen's parser to use Text::Balanced rather than split.

Rework risugen's parser to use Text::Balanced; this opens the way
for a generalisation of the format to labelled brace-marked blocks,
so we can specify load/store memory usage as well as constraints.

stsquad/risu,vivier/risu,hw-claudio/risu-aarch64,vivier/risu,stsquad/risu,stsquad/risu,hw-claudio/risu-aarch64