precedence: set default production precedence using bison protocol

Signed-off-by: Peter Williams <pwil3058@gmail.com>
conflict: change conflict resolution bias against error to include lexError

Signed-off-by: Peter Williams <pwil3058@gmail.com>
conflict: do bison/yacc default conflict resolution but require approval.
Shift/reduce conflict resolved in favour of shift.
Reduce/reduce conflict resolved in favour of first production defined.
Require user to specify the number of conflicts that are acceptable.
It's their responsibility to inspect the grammar to justify their decision.

Signed-off-by: Peter Williams <pwil3058@gmail.com>
readme: hopefully a more useful README

Signed-off-by: Peter Williams <pwil3058@gmail.com>