All tools should have a -h/--help option

[kba]

Not all the tools support a help flag. We should add this as a baseline so users can get at least minimal usage info on the command line.

Tools without -h/--help (c.f. smoke.tsht):

• hocr-check
• hocr-combine
• hocr-extract-images
• hocr-lines
• hocr-merge-dc

Plus possibly those that do not run at the moment because of PyXML/lxml #9

[zuphilip]

Moreover, we can check that the help will be shown, if a command is called without any argument. I am not sure how consistently this is already the case at the moment.

[kba]

Some commands expect to read from STDIN and will just wait for input if no argument is given.