Move to liblightgrep 1.2.1 from 1.2.0.
The base16 scanner never added any digits to the CharClass it was
supposed to be filling---hence the scanner did a lot of work but was
ultimately a no-op. Fixed.
base16 flex scanner pattern no longer has leading context, so hits start
at pos, not pos+1.
Merge pull request #45 from uckelman/be_pull

Move to liblightgrep 1.2.1 from 1.2.0 & fix two bugs in scan_base16.flex.