Fix remaining GPLv3 header (closes #221)
Update license for the tests in Debian packaging (#221)
unit-test-client: fix compilation on compilers not supporting c99 mode

This fixes the message
"error: 'for' loop initial declarations are only allowed in C99 mode",
spotted during cross-compiling of libmodbus.

The compiler (gcc) actually does support -std=c99 but it gets not
enabled by default. So a solution would be to enforce c99 mode
via CFLAGS, but this will knock out all compilers which do not
support this mode.
Moving the declaration out of the loop initialisation, seems to be
the simpler solution.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>
Prefix hexadecimal values with 0x to avoid confusion
Don't flush on illegal address errors in single write functions

This change has introduced by 83c34102.
Fix unit tests on some systems.
Fix wrong usleep value to wait 5 ms between bytes in test server
Fix too low response timeouts in unit tests

The response timeout of the client must be higher than the server
to handle sleep/flush operations done on server side.
Updated NEWS file
Rewrite documentation macro and Makefile

- only check if documentation tools are installed in acinclude.m4
- don't provide built documentation in dist tarball
- simpler Makefile
- display warning message and check result
Minor adjustments to README.md about documentation
doc: generate manual pages with a2x
doc: slight change in asciidoc config file to print vX.Y
Add some more macros for data manipulation

Signed-off-by: Michael Heimpold <mhei@heimpold.de>