parsetoml: support compiling with strictFuncs again

[ee7]

Nim 1.6.0 added an opt-in for the strictEffects behavior, which will become the default in Nim 2.0.

Commit bb90361 allowed Nim to compile parsetoml with strictEffects, but we could no longer compile with strictFuncs:

$ nim c --experimental:strictFuncs src/parsetoml.nim
/tmp/parsetoml/src/parsetoml.nim(1742, 6) Error: '==' can have side effects
> /tmp/parsetoml/src/parsetoml.nim(1769, 22) Hint: '==' calls `.sideEffect` '[]'
>> /foo/nim-devel/lib/pure/collections/tables.nim(1851, 6) Hint: '[]' called by '=='

Add an override so that strictFuncs doesn't complain about the func. Simply changing the func to a proc doesn't work.

Note that the definition of strictFuncs was recently changed.

Closes: #61

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I've checked that this works for every combination of strictEffects and strictFuncs, with both Nim 1.6.12 and devel. I don't know if we want to make a change in times.nim too, but I think we want this PR either way (so that we can compile parsetoml with strictFuncs without waiting for a new Nim release).

[ee7]

@PMunch Could you please take another look at this? It should be safe as a workaround, even if there may or may not be a better change in upstream std/tables.

I've checked that nim c --experimental:strictFuncs src/parsetoml.nim doesn't work with Nim 2.0.

[ee7]

Thanks.