build: Add --disable-adl-checks

Requested in https://github.com/veox/sgminer/issues/26

configure.ac needs an overhaul (see SDMINER_SDK).
build: reorder ADL checks.

If `--disable-adl-checks` is given, enable ADL immediately.
cross-compile: comment out sleep().

Reported as unneded:
https://github.com/veox/sgminer/issues/37

When is this true? Which IDEs, Windows/MinGW versions?
Add some notes about cross-compiling cgminer for Windows from Linux
doc: revert some formatting changes made by Drogean to windows-build.txt
Add clarification on Windows cross-build, out of tree is possible
doc: Simplify paths for cross-compiling instructions in windows-build.txt
misc: line wrap.
adl: only ask for iDrvIndex on Linux.

Should close https://github.com/veox/sgminer/issues/45
doc: add note about --disable-adl-checks.

Should close https://github.com/veox/sgminer/issues/26
Merge branch 'windows-cross-compile'
VS2010 build: prepare ADL.

Cherry-picked by veox.
VS2010 build: prepare API.

Cherry-picked by veox.

Previous variable 'new' was badly named, but troky's 'n' was too cryptic.
Therefore renamed to 'newsize'.
VS2010 build: ccan/opt

Cherry-picked by veox.
VS2010 build: Prepare compat/jansson-2.5.

Cherry-picked by veox.

Not a big fan of modifying compat libraries, makes it harder to maintain
later on. See if these changes are relevant upstream.
VS2010 build: Prepare driver-opencl.c.

Cherry-picked by veox.

Changes from troky: struct device_drv opencl_drv tab alignment.
VS2010 build: Prepare findnonce.c

Cherry-picked by veox.
VS2010 build: Prepare hexdump.c

Cherry-picked by veox.
VS2010 build: Prepare miner.h

Cherry-picked by veox.
VS2010 build: Prepare ocl.c

Cherry-picked by veox.