Add MakeWeights and fix some issues with procedures

[junyuan-chen]

No description provided.

[codecov]

Codecov Report

Merging #2 (d79bd51) into master (49038c7) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master       #2   +/-   ##
=======================================
  Coverage   99.55%   99.56%           
=======================================
  Files           8        8           
  Lines         452      456    +4     
=======================================
+ Hits          450      454    +4     
  Misses          2        2           

Impacted Files	Coverage Δ
src/DiffinDiffsBase.jl	100.00% <ø> (ø)
src/utils.jl	100.00% <ø> (ø)
src/StatsProcedures.jl	99.17% <100.00%> (ø)
src/procedures.jl	100.00% <100.00%> (ø)
src/terms.jl	100.00% <100.00%> (ø)

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