hantek-dso: use per-device firmware filenames
Doxygen: Fix a few warnings.
Doxygen: Properly document and handle version.h.
Doxygen: Exclude std.c and tests/*.

These don't contain any public API functions or macros and thus should
not appear in the ("public API" version of) the Doxygen docs.
hantek-dso: cosmetics
Fix kernel driver attached check

The check is really only broken on darwin, but useful on all other
platforms, even if only Linux can actually detach a driver.
configure.ac: Improve pkg-config related checks.

Until now, we checked for certain (optional) libraries via pkg-config and
the configure script would abort if any of them was not found, even
though they were optional. It was up to the user to then figure out which
combination of --disable-<drivername> switches were required for his
specific OS (and set of installed libs) to get a working configure run.

Only if the user already specified enough --disable-<drivername>
switches beforehand, so that all drivers which require a missing library
were disabled, would the configure run not check for that specific lib
(and would thus not fail).

With this change, we now always unconditionally check for all libs
(required and optional) via pkg-config. However, whether an (optional) lib
is found or not, configure will not abort. Instead, it'll just disable
all drivers which need a lib that cannot be found.

The user will no longer have to supply --disable-<drivername> parameters
in order to get a working build.
configure.ac: Fix the order of some entries.

In order for lib autodetection and disabling of drivers (which require
libs that cannot be found) to work, the order of AC_ARG_ENABLEs,
AM_CONDITIONALs, and AC_DEFINEs needs to be changed.

All drivers start out enabled or disabled (depending on whether
the --disable-drivers option was supplied or not). Then, any driver can
be enabled or disabled explicitly via --enable-<drivername> or the
resp. --disable-<drivername> option. Finally, pkg-config checks for all
libraries are performed, and all drivers which require a library that
cannot be found are disabled explicitly (regardless of any
--enable-<drivername> option that might have been supplied).
configure.ac: Improve USB/EZUSB/serial checks.

 - If libusb-1.0 is not found, do not compile in ezusb.c and usb.c since
   they require libusb.h. The respective hardware drivers that use
   libusb-1.0, and usb.c and/or ezusb.c will be excluded from the build
   elsewhere in configure.ac. Rename NEED_EZUSB to NEED_USB.

 - Drop the NEED_SERIAL check and always compile in serial.c. This is a
   very small chunk of code, it does not depend on any external
   libraries that might be missing, and it compiles on all architectures.
   Thus there's no need to conditionally include or exclude it.
configure.ac: Improve a libusb-1.0 related check.

Don't rely on the "heuristic" that 'libusb_CFLAGS' will be non-empty if
libusb-1.0 was found, but rather use the proper method of checking the
variable 'have_libusb1_0' which pkg-config will set to "yes"/"no"
depending on whether it finds the library.
configure.ac: Cosmetics for the list of drivers.

Use the canonical driver name (all-lowercase, e.g. "serial-dmm") in the
list of enabled/disabled drivers that configure prints after a run.

It's common to many drivers that they support multiple devices, so
printing one device name (e.g. "ChronoVu LA8") is seldom really correct.
E.g. the agilent-dmm, asix-sigma, brymen-dmm, colead-slm, fluke-dmm,
fx2lafw, hantek-dso, lascar-el-usb, mic-985xx, openbench-logic-sniffer,
rigol-ds1xx2, uni-t-dmm, victor-dmm, and zeroplus-logic-cube drivers
all support more than just one device.

So, just print the driver name instead which is more correct anyway
since it's specifically a list of enabled/disabled drivers.
configure.ac: Only enable rigol-ds1xx2 on Linux.
configure.ac: Mention required lib versions.

In the summary output at the end of a configure run, explicitly mention
which versions of which libraries are required, and also the version which
pkg-config has found.
configure.ac: Print $host and $build.

In the configure summary at the end also print the architecture we're
building on ($build) and the target host we build for ($host). The two are
not necessarily the same, e.g. in the case of cross-compiles.
vcd output: Build fix for Windows/MinGW.

On Windows/MinGW 'recv' seems to be already defined in windows.h/winsock2.h.

Use 'receive' instead, for now, otherwise we get an error:

vcd.c:147:17: error: conflicting types for 'recv'
configure.ac: Fix checks for cross-compiles.

When checking architecture-specific things, always check $host, i.e. the
architecture we're building _for_, not the one we happen to build _on_.

E.g. when cross-compiling _for_ Android (or Windows or others) it's important
to check for Android in $host; whether we happen to cross-compile _on_ a Linux
or Windows or OpenBSD or FreeBSD machine ($build) doesn't matter, only the
fact that we compile _for_ Android is important for most checks.
Bump copyright year
Use GVariant for sr_config_*() functions

sr_config_get() provides a GVariant owned by the caller, so it must be
released with g_variant_unref() when done.

sr_config_set() takes a GVariant from the caller which may be floating;
it will be properly sunk and release after use by this function. Thus
the output of g_variant_new_*() may be used as an argument.

sr_config_list() also provides a GVariant owned by the caller, to be
unreferenced when done.

sr_config_make() can take a floating reference.
Adjust to GVariant-based sr_config_* functions
Add sr_config_free()

Due to struct sr_config now containing a GVariant, this needs to be
cleaned up after use properly. This is a helper function for that.