add usage and required args to -h output

[Ivan Beschastnikh]

Need to add this:

Usage: texada [opt1] ... [optN] log-file

Required options: -f, log-file, one of [-l, -m, -p]

at the top of the printout for/no args output.

[Issue created by carolemieux: 2015-08-21]

[Comment created by carolemieux: 2015-08-21]
resolved in 03c5d0b65105

[Comment created by carolemieux: 2015-08-21]
fix issue69

→ <<cset 03c5d0b65105>>