Reorganize API

[avh4]

• fillInTextArea: this is kind of weird -- maybe should be renamed to be more specific (fillInPrimaryTextArea)?
• check: capybara has check vs uncheck instead of taking a Bool
• simulate: this should be more specific to DOM now -- maybe simulateDomEvent? but will that name be confusing after adding simulation for Browser.Events (I guess that would be simulateBrowserEvent)?
• within

https://docs.google.com/spreadsheets/d/1Z2M4RoameHD9hyEELpTdRrkIx4rLxJS9ifVoMc4IQjE/edit?usp=sharing

[avh4]

Some changes that seems pretty clear:

• assertHttpRequestWasMade -> expectHttpRequestWasMade
• assertHttpRequest -> shouldHaveMadeHttpRequest
• assertAndClearOutgoingPortValues -> shouldHaveOutgoingPortValues

[avh4]

Replaced by https://github.com/avh4/elm-program-test/pull/59