[DTable] Leftjoin

[krynju]

• leftjoin generic for any Tables.jl type
• innerjoin generic for any Tables.jl type
• inner matching passes with different kwargs for optimization (r_sorted, l_sorted, r_unique)
• fallback to specialized methods (e.g. dataframes will use its own joins internally)
• support for passing lookup tables to quickly match indices using a hash table for example
• outerjoin research - answer: it's possible but not really nice of a solution, so skip for this PR
• how to handle dtable x dtable joins? - answer: it works, but not necessairly the optimal way of doing it

[codecov-commenter]

Codecov Report

Merging #287 (8b4c042) into master (d06eb91) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master    #287    +/-   ##
=======================================
  Coverage    0.00%   0.00%            
=======================================
  Files          40      42     +2     
  Lines        3317    3488   +171     
=======================================
- Misses       3317    3488   +171     

Impacted Files	Coverage Δ
src/Dagger.jl	0.00% <ø> (ø)
src/table/dtable.jl	0.00% <ø> (ø)
src/table/join.jl	0.00% <0.00%> (ø)
src/table/join_interface.jl	0.00% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d06eb91...8b4c042. Read the comment docs.

[jpsamaroo]

Great work!