Increase the default LPeg stack size.

It is not clear how large this value should be. It appears to be a function of grammar complexity.

For example, a problematic HTML file requires a value of 1329 to work, but removing either the
'attribute' rule or an embedded lexer reduces the limit.

However, identifying which files trigger a stack overflow is not trivial. It does not appear to
depend on file size. For example, the problematic HTML file is 125K, but a non-problematic HTML
file of 500K works.

lexers/lexer.lua

@@ -781,6 +781,8 @@ local lpeg = lpeg
 local P, R, S, V, B = lpeg.P, lpeg.R, lpeg.S, lpeg.V, lpeg.B
 local Ct, Cc, Cp, Cmt, C = lpeg.Ct, lpeg.Cc, lpeg.Cp, lpeg.Cmt, lpeg.C
 
+lpeg.setmaxstack(1328) -- the default of 400 is too low for complex grammars
+
 --- Default tags.
 local default = {
   'whitespace', 'comment', 'string', 'number', 'keyword', 'identifier', 'operator', 'error',