Add parameters option to parse

[blakeembrey]

Some packages, such as type-is, only need the type from the header and don't use the parameters. Passing parameters: false in those cases uses the faster path by exiting early which is 10X faster with just a couple of parameters.

[blakeembrey]

Some readability tweaks in case we want to expose parseParameters later. No change in overall performance by making this change now.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a23924a) to head (d2d175d).

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #61   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          107       112    +5     
  Branches        40        41    +1     
=========================================
+ Hits           107       112    +5     

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