Support geohash API(#14)

[wangjian-pg]

Support the redis geohash API(#14). The implementation is derived from the C code of Redis.

[codecov]

Codecov Report

Merging #28 into master will increase coverage by 0.14%.
The diff coverage is 49.81%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
+ Coverage   51.07%   51.21%   +0.14%     
==========================================
  Files          95       99       +4     
  Lines       15367    16346     +979     
==========================================
+ Hits         7848     8371     +523     
- Misses       6229     6631     +402     
- Partials     1290     1344      +54

Impacted Files	Coverage Δ
common/geohash/type.go	0% <0%> (ø)
node/node_cmd_reg.go	100% <100%> (ø)	⬆️
common/geohash/util.go	23.03% <23.03%> (ø)
node/geo.go	63.25% <63.25%> (ø)
common/geohash/geohash.go	83.63% <83.63%> (ø)
transport/rafthttp/peer.go	75.57% <0%> (-1.53%)	⬇️
transport/rafthttp/stream.go	80.13% <0%> (-1.31%)	⬇️
node/raft.go	40.41% <0%> (-0.13%)	⬇️
... and 9 more

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[absolute8511]

LGTM

[absolute8511]

Will be merged after the next release.