add ImportDeclaration constructor
add ImportDeclaration parser
use ModulePath instead of [ProperName]
add Alias constructor to NameKind

This is so that someone smarter/more familiar with the code-base than I
can change the current aliasing behavior so it doesn't have to create
actual `var`s.
add ImportDeclaration type checker
implement declToJs for ImportDeclarations

This changes `declToJs` so it takes an Environment parameter as well.
fix hlint warning in parseImportDeclaration
add passing import test
add failing import example