If a .tool-versions file did not end with a newline new tools and
versions would get appended to the same line rather than properly
added on a new line in the file
Fixes#1299
* fix: always use ASDF_DEFAULT_TOOL_VERSIONS_FILENAME for filename when present
* fix: correct version command unit tests for ASDF_DEFAULT_TOOL_VERSIONS_FILENAME
Fixes#1082
* fix: don't invoke asdf inside asdf commands
Recursive calls have a number of disadvantages:
* Poorer performance since each invocation spawns and new process and re-executes all the code in bin/asdf
* Makes debugging more difficult
* More likely to introduce subtle bugs and the possibility for infinite loops
