Support span:// for Cloud Spanner scheme

[k1LoW]

No description provided.

[codecov]

Codecov Report

Merging #133 into master will decrease coverage by 1.19%.
The diff coverage is 0%.

@@           Coverage Diff            @@
##           master    #133     +/-   ##
========================================
- Coverage   70.59%   69.4%   -1.2%     
========================================
  Files          12      12             
  Lines        2585    2585             
========================================
- Hits         1825    1794     -31     
- Misses        587     624     +37     
+ Partials      173     167      -6

Impacted Files	Coverage Δ
datasource/datasource.go	21.25% <0%> (-19.38%)	⬇️

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