squirrel3: Update to Squirrel 3.0.6 stable
squirrel3: Allow floating number literal starting with dot for lexer

Squirrel language does not support floating number literals beginning
with a dot, e.g. ".12", ".001" or ".5e3", although C language family
support them.  This is an attempt to modify Squirrel lexical scanner
to accept those literals.

I think this change won't affect existing syntax since a token
beginning with a dot and a digit became an immediate error.
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