Clarify that the currently supported version of the API is 2 and that the preferred method for selecting it is sending a SetApiVersion command after connection. Fixes #2066
* Initial implementation for 'dlv dap' * Fix Travis and AppVeyor failures * Address review comments * Address review comments * Regenrate documentation * Replace dap server printfs with log.Error * Update 'dap log' * Fix typos * Revert logflags changes that got mixed in by accident