Yul keywords are to greedy

[mbenke]

ben@trawa:~/work/solcore$ cat tmp/yulkw.solc
function bad() -> () {
   format : word
   assembly {
     format := 0
   }
}ben@trawa:~/work/solcore$ cabal exec sol-core -- -f tmp/yulkw.solc 
error[SC0001]: parse error: unexpected 'm'
  ──> /home/ben/work/solcore/tmp/yulkw.solc:4:9
  │
4 │      format := 0
  │         ^ unexpected token

Proposed fix:

pKeyword is not backtracking:

pKeyword w = lexeme (string w <* notFollowedBy identChar)

change to

pKeyword w = lexeme (try (string w <* notFollowedBy identChar))