sr_init(): Sanity-check input/output modules.
ols: use ptr to int dereference for SR_T_BOOL

This mad ptr to int casting has to go.
add SR_CONF_DATALOG
lascar-el-usb: support for SR_CONF_DATALOG
configure.ac: Add missing AM_PROG_CC_C_O.
Add initial README.devices file.
add SR_CONF_SAMPLE_INTERVAL

Expresses the time between samples, in milliseconds. This can be used
for devices with a samplerate > 1 second, such as dataloggers, which
cannot be expressed with SR_CONF_SAMPLERATE.
lascar-el-usb: push samplerate before data log
autotools: Don't use "foreign" option.

This adds INSTALL and allows for a few more sanity checks being done.
README: Refer to INSTALL and new Building wiki page.
Don't make README.devices executable.
configure.ac: Drop std-options, unneeded.

The automake 'std-options' option checks whether all installed tools
and scripts have a --help and --version CLI option. This check is not
needed for libsigrok though, since it doesn't install any tools.
configure.ac: Add 'color-tests' (colorized 'make check').
serial.c: FreeBSD and OpenBSD don't have OFILL either.
set proper build defaults for brymen-dmm and mic-985xx drivers
alsa: Set the probe index
fx2lafw: Partial Revert of b99457f0

The original patch replaced a few cases where variables were
declared and initialised mid-function. Some of these were consts,
which were removed. Others were variable which could be made const
but have not been.

There have been some concerns raised about the readability of
variables/consts declared mid-way through functions. I believe
these are overblown. Certainly not of great enough significance
to warrent the wholesale removal all of these.

consts are an important protection offered by the C language, and
are a useful constraint for optimizers to exploit. They also
show new readers of the code that the variable is not reassigned
later, they also prevent later modifications to code from using
a variables in ways they were not intended to be used.

By definition a const can only be declared when it's value is
available - and this is often only possible mid-way though. This
is a legitimate reason to justify variables not always being
declared at the start of functions.

b99457f0 removed const declarations which this patch reintroduces.
It also removed variables decared mid-function - in each of these
latter cases these variables can be made const. A following patch
will make this change because any constraint that can be used
should be used, because stricter more tightly defined code is
always beneficial.
fx2lafw: Made variables const
fx2lafw: Added support for AX analog channel probing
fx2lafw: Factor packet send into a selectable send_data_proc handler