Rename insecureTLS to skipVerifyTLS

Rename `insecureTLS` to `skipVerifyTLS` to make it clearer what this
flag does. Also clarify the flag description.
Fix variable alignment
Rename `insecureTLS` in README

As per the changes in 1e73e524aed3445f45a81915c3f0c44787379dc0.
Merge pull request #15 from alphagov/clarify-insecure-flag

Rename insecureTLS to skipVerifyTLS