This PR saves some memory by ommiting redundant output. The printing
of "jumpint into first task..." is obsolete, as the thread_create
calls are not checked for errors anymore.

Further the version print is moved into the main_trampoline. This
prevents the STDLIB from using precious stack space on the ISR
stack, on which it is running before jumping into main - hence
opening the option to decrease the stacksize for the ISR stack.

As discussed in #2725, this commit renames a number of stacksize constants to
better convey their intended usage. In addition, constants for thread priority
are given a `THREAD_` prefix. Changes are:

* KERNEL_CONF_STACKSIZE_PRINTF renamed to THREAD_EXTRA_STACKSIZE_PRINTF
* KERNEL_CONF_STACKSIZE_DEFAULT renamed to THREAD_STACKSIZE_DEFAULT
* KERNEL_CONF_STACKSIZE_IDLE renamed to THREAD_STACKSIZE_IDLE
* KERNEL_CONF_STACKSIZE_MAIN renamed to THREAD_STACKSIZE_MAIN
* Move thread stacksizes from kernel.h to thread.h, since the prefix changed
* PRIORITY_MIN renamed to THREAD_PRIORITY_MIN
* PRIORITY_IDLE renamed to THREAD_PRIORITY_IDLE
* PRIORITY_MAIN renamed to THREAD_PRIORITY_MAIN
* Move thread priorities from kernel.h to thread.h since the prefix has changed
* MINIMUM_STACK_SIZE renamed to THREAD_STACKSIZE_MINIMUM for consistency

There's no need to run config_load from core directly, can be done by
auto_init.

Building MSP boards gives an error, because `VERSION` is somewhere
defined in their toolchain as an integer.

This PR renames `VERSION` into `RIOT_VERSION`, because that's what it
is.

Eliminates special treatment of the hwtimer module and makes it a
mandatory part of the kernel.

The function sched_init() zeroes out sched_threads needlessly. All
static variables can be assumed to be initialized with zero, anyways.
The C standard mandates it, and all at other places in the code it is
assumed.

kaspar.schleiser@fu-berlin.de is obsolete.
(2nd try, first try was overwritten by some overzealous documenter)

kaspar.schleiser@fu-berlin.de will be obsoleted soon. Replace it with
kaspar@schleiser.de, which will (hopefully) stay.

This reverts commit 69c526f4.

Instead of removing ENABLE_DEBUG, define it as zero and replacing the
ifdef preprocessor commands by a simple #if

german "intern" to english "internal"

this fixes some compiler warnings