Fix for exception caused by float specials and support for 2 more operators

- Added `$each` and `$slice` modifiers for `$push` operator
- Added decoding for `$near` operator (for simple 2d queries).
- For complex 2d queries there's a `$geoNear` command which can be invoked by `mongoapi:runCmd(...)`
This command returns some statistics. And I ran into a problem when one of the fields in those stats may be NaN. And Erlang does not support float special values like NaN, +/-Inf, +/-0. Trying to match it causes exception. I added a simplest workaround and you may want to match those values directly by specifying them, although I don't know what to return in those cases - right now I left it to int 0 for any special value.