RFC 001: Cancelable operations and use of Context

[asdine]

This PR adds an RFC about how we should use Context in Genji.

It is opened for comments and suggestions.

[codecov-io]

Codecov Report

Merging #249 into master will decrease coverage by 0.82%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #249      +/-   ##
==========================================
- Coverage   61.61%   60.78%   -0.83%     
==========================================
  Files          67       68       +1     
  Lines        6273     6579     +306     
==========================================
+ Hits         3865     3999     +134     
- Misses       1895     2060     +165     
- Partials      513      520       +7     

Impacted Files	Coverage Δ
engine/memoryengine/store.go	91.96% <0.00%> (-1.79%)	⬇️
sql/parser/options.go	100.00% <0.00%> (ø)
sql/query/expr/function.go	6.55% <0.00%> (+0.82%)	⬆️
sql/parser/expr.go	80.95% <0.00%> (+2.67%)	⬆️
sql/parser/parser.go	87.68% <0.00%> (+4.70%)	⬆️

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[tie]

I think parser.ParseQuery shouldn’t accept context (it does so now). Parsing statements shouldn’t be an expensive operation.

[asdine]

@tie @yaziine Do you see any blocker for this RFC?

[yaziine]

Everything seems fine to me. 👍

[tie]

One last suggestion, everything else looks great!