Detect non-leading tabs

Tabs are only used for indent and should not be used elsewhere in source.
Otherwise the source won't look correct with different tab widths.
Non-leading tab fixes
Non-leading tab fixes
Merge branch 'code-policy-nonleading-tabs'
Performance overview to performance section
Merge branch 'guide-perf-expectations'
Ditz issue update
Add JSON number decode test
Merge branch 'add-json-exp-testcase'
Don't #error when SIZE_MAX is < 0xFFFFFFFFUL

There are some systems where SIZE_MAX is less than that even when the
platform is a 32-bit one.  It's probably not useful to error out because
Duktape only uses SIZE_MAX for assertion(s) (only one assert right now).
Release note: SIZE_MAX check
Merge branch 'remove-size_t-check'
Ditz issue update