prevent rounding 0 if HWTIMER_SPEED > 1000000L

The current macros in hwtimer.h expect HWTIMER_SPEED to be < 1000000L, otherwise integer arithmetic will round the result down to 0.
Add a case to prevent that.
doc: added missing closing doxygen brackets
doc: use @brief for single defines
doc: added missing titles
doc: fixed typos and other misspellings
doc: use @false instead of 0
doc: use doxygen li tags
doc: add to group instead of redefining
doc: fix typo in UDP header
doc: remove doxygen duplication
doc: removed broken doxygen struct tags
doc: removed superfluous (and broken) @file params
doc: fixed broken param descriptions
cpu: msp430: renamed msp430x16x to msp430fxyz
cpu: lpc2387: integrated lpc_common into lpc2387

Rationale 1: The common part made only sense for (some) NXP ARM7 MCUs,
but was misleading for MCUs like the LPC1768.

Rationale 2: The common part was only used by one specific MCU
implementation - no need to outsource it.
core/thread: use disableIRQ/restoreIRQ
doc: document internal cib init macro
Merge pull request #2138 from OlegHahm/doxygen_fix_core_warnings

doc: document internal cib init macro
doc: add some references
Merge pull request #2108 from LudwigOrtmann/thread_new_irq_api

Thread new IRQ api