Split hothouse to internal packages

[Leko]

This PR fixes #8 and fixes #7 and fixes #6.

[codecov-io]

Codecov Report

Merging #10 into master will decrease coverage by 0.54%.
The diff coverage is 28.57%.

@@            Coverage Diff             @@
##           master      #10      +/-   ##
==========================================
- Coverage   27.27%   26.73%   -0.55%     
==========================================
  Files           1        5       +4     
  Lines          11      101      +90     
  Branches        3       18      +15     
==========================================
+ Hits            3       27      +24     
- Misses          7       63      +56     
- Partials        1       11      +10

Impacted Files	Coverage Δ
packages/hothouse/src/Package.js	27.27% <ø> (ø)	⬆️
packages/@hothouse/client-npm/src/index.js	13.04% <14.28%> (ø)
packages/@hothouse/monorepo-lerna/src/index.js	21.05% <22.22%> (ø)
packages/@hothouse/client-yarn/src/index.js	33.33% <25%> (ø)
...es/@hothouse/monorepo-yarn-workspaces/src/index.js	38.88% <38.88%> (ø)

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