Fix circular bundles, and never hoist the entry asset

[devongovett]

Slightly simpler, more generic version of #489.

There were two issues:

1. Infinite recursion on circular bundles. This is solved by tracking the current bundle stack.
2. HTML files getting merged into one bundle. This was because Parcel tried to hoist the common dependencies. However, this should never be done for the entry asset of a bundle since those assets were explicitly requested to be placed in a separate bundle (deps marked as dynamic).

Added test covers both cases. cc. @shawwn @ipmb

[codecov-io]

Codecov Report

Merging #548 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #548      +/-   ##
==========================================
- Coverage   88.36%   88.34%   -0.02%     
==========================================
  Files          56       56              
  Lines        1633     1639       +6     
==========================================
+ Hits         1443     1448       +5     
- Misses        190      191       +1

Impacted Files	Coverage Δ
src/Bundler.js	88.88% <100%> (+0.26%)	⬆️
src/utils/installPackage.js	87.5% <0%> (-6.25%)	⬇️

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[ipmb]

works for me!