Refactor Exports, Add UTF-8 Tests

[kristoferbaxter]

This is a long awaited refactoring of export support to make it easier to add additional support in the future.

Additionally, this PR adds a test for UTF8 imports.

[codecov-io]

Codecov Report

Merging #277 into master will increase coverage by 0.07%.
The diff coverage is 96.98%.

@@            Coverage Diff             @@
##           master     #277      +/-   ##
==========================================
+ Coverage   96.44%   96.52%   +0.07%     
==========================================
  Files          18       20       +2     
  Lines        1520     1667     +147     
  Branches      141      154      +13     
==========================================
+ Hits         1466     1609     +143     
- Misses         51       55       +4     
  Partials        3        3

Impacted Files	Coverage Δ
src/index.ts	89.58% <100%> (+0.81%)	⬆️
src/parsing/preserve-named-constant-export.ts	100% <100%> (ø)
src/transformers/strict.ts	96.77% <100%> (ø)	⬆️
src/parsing/preserve-default-export.ts	100% <100%> (ø)
src/temp-file.ts	96.42% <100%> (ø)	⬆️
src/parsing/literal-name.ts	100% <100%> (+4.54%)	⬆️
src/compiler.ts	98.07% <100%> (+0.03%)	⬆️
src/options.ts	95.48% <100%> (+0.06%)	⬆️
src/parsing/import-specifiers.ts	100% <100%> (+4.16%)	⬆️
src/transformers/imports.ts	97.18% <100%> (ø)	⬆️
... and 8 more

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