doxygen: documentation hierarchy fixes

Also remove doc.txt for sam3 (moved to cpu_conf.h)

cpu/kinetis_common: Cast device index enums to unsigned int before comparing for out of range values

sys/net/network_layer/ng_sixlowpan/iphc: Set IPv6 header length after decoding

cpu/kinetis_common: Cast device index enums to unsigned int before comparing for out of range values

Suppresses false warning in Clang:

    warning: comparison of constant 42 with expression of type 'xxx_t'
    is always false [-Wtautological-constant-out-of-range-compare]

See:
 - https://llvm.org/bugs/show_bug.cgi?id=16154
 - https://llvm.org/bugs/show_bug.cgi?id=22062

ng_ndp, fib: Two small code style fixes

Explain how to connect RIOT to Linux

doxygen: add make targets to build man and latex

libcoap: switched to new "official" Github repo

HTML will be build per default.

drivers/hih6310: Initial commit of HIH6310 driver

Honeywell HumidIcon Digital Humidity/Temperature Sensors: HIH-6130/6131 Series

Only basic humidity and temperature measurement support is implemented.

Missing:
 - Alarm interrupts
 - Command mode (reconfigure i2c address, alarm levels, alarm polarity, custom ID)

libcoap: switch to the RIOT-OS mirror

od: signedness and constantness of input parameter

Makefile.include: Add --cref to linker options

aodvv2: tidy debug output, remove VDEBUG(), add LOG()

fib: check dst and next_hop for invalid pointers

doxygen: Clean up groups for msp430 and arm7

ng_sixlopan_iphc: Multicast decoding 8-bit fix and build fix

pkg/libfixmath checkout fixes

doc/doxygen/riot.doxyfile: Do not generate man/LaTeX by default