app.{Common,demux}: make gzip options global

While starting to port other sub-commands to the common options it
became obvious that passing all those arguments was not scalable. The
`Global_configuration` module contains *global* references but at least
provides and unified API.
app: move I/O buffer-sizes to Global_configuration
app.random: homogenize command line (App_common)
Common: fix function file_to_file (use config)
Common: improve Command_line.gzip_output_flags
app.transform: use Command_line.gzip_output_flags
app.random: add verbosity flags
app.Common: add code documentation
app.demux: move help message to option `-manual`
app.demux: improve the `more_help` function
app.demux: document the code
app.demux: add CL option `-exclusive-demux`
app: clean debug messages
App_common.Say: add colored output and word_wrap
App_common,app.demux: add `Say.raw`
app.demux: improve manual
app.demux: add contents of `-help` to `-manual`
App_common: move markdown code to Text.Markdown
App_common: factor the `display_manual_flag`
App_commong: factor common sections into Markdown