Added support for unix nano and milliseconds

[edyesed]

Hi,
This library is very useful to me. However, I needed support for Unix epoch-seconds time format with millisecond and nanosecond granularity.

• I've added support for unix epoch-seconds will millisecond and nanosecond granularity. ( with tests )
• I added the time.Time type and options to the example struct in README.md as well.

[codecov]

Codecov Report

Merging #44 (388d592) into master (55faf79) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #44   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          112       116    +4     
=========================================
+ Hits           112       116    +4     

Impacted Files	Coverage Δ
query/encode.go	100.00% <100.00%> (ø)

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[willnorris]

this looks straightforward enough, thanks for the contribution! A few small changes (which I'll just go ahead and make and submit right after this comment)...

• rename options to "unixmilli" and "unixnano" for naming consistency both with the "unix" option as well as the time.UnixNano() method
• add documentation for these new options to the package godoc
• remove the README changes (see Add more examples into README.md #43 for similar discussion), but add a link to the package godocs. I'd ideally prefer to just inline more examples in the godocs, which then keeps all the documentation together. Or possibly just provide a couple of additional advanced examples in the README without changing the simple one that's already there.

[dgsdoug]

@@ Coverage Diff @@

master #44 +/-

=========================================
Coverage 100.00% 100.00%

Files 1 1
Lines 112 116 +4

• Hits 112 116 +4