Let Prettier infer the parser when it can

[lassik]

Alternative impelementation of PR #195

See also:

• Issue Possibility of removing the prettier parser arguments, or add the ability to configure your own #175
• PR fix: let prettier select parser automatically only when it succeeds #190, fix: rely on prettier to choose the correct parser #182

[lassik]

@liuyinz Here's an alternative implementation of the approach you used in PR #195. It adds a bit more robustness (though we are still using a regexp). Can you check whether this works for you?

[lassik]

Sorry, I botched the initial PR. Now tested. Also added a debug message showing the full --file-info output.

[liuyinz]

Tests good. Merge? @lassik