libpcp_web: increase default JSON parser token count
libpcp_web: increase default JSON parser token count

Diagnostics from code using the JSON parsing shows the
default value of 16 tokens to be quite low, causing us
to re-parse unnecessarily - bump it up to 128 tokens,
which reduces all of the observed cases to single-pass
parsing.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp