Type and runtime checks for default and validOptions combos

[lukekarrys]

This PR does a few things in the name of increasing type and runtime checks for fields with the full combination of default and validOptions across different type and multiple combinations. Fixes #17

Some other notable items:

• Refreshes the lockfile
• Removes the parseArgs shims since all supported Node versions have it natively
• Creates a new test file to test all these scenarios
• Reorders index.ts so all types are at the top with isType functions below their type counterpart
• Consolidate the types and code paths for initializing fields via addFields/opt/optList/num/numList/flag/flagList so they all get the same behavior

Some possible breaking changes due to some of the above refactoring:

• type MultiType is gone since it was no longer needed in the same way
• Renamed type ConfigOptionBase is now type ConfigOption. This is maybe a bit arbitrary but I think matches better to how it is used.
• Changed the optional/required-ness of some generic type arguments

[lukekarrys]

TODO:

• export all types
• fix how this handles the case of multiple:true with default values not being narrowed properly
• fix case where flags with defaults are made optional