Blech compiler creates subdirectory `blech` even without an input file

[schorg]

If blechc is called without an input file or with the name of an input file that cannot be found Calling blechc creates a subfolder blech for generated compilation results.
This also happens if no input file is given or the input file cannot be found.

This behavior is a little bit unfortunate because it may create folders named blech anywhere when blechc is called.

Proposal: Only create the subfolder blech in a project directory, when the input file is found or given.