doc: add some references
rpl: removing unnecessary recv_mutex

In the main function of RPL (rpl_process thread)
a mutex is used after receiving a message via msg_recv.
However, this mutex is never used in another thread and thus is rendered
obsolete.
Merge pull request #2139 from OlegHahm/doxygen_fix_core_warnings

doc: core: sched: add some references
Merge pull request #2147 from cgundogan/rpl_unnecessary_mutex

rpl: removing unnecessary recv_mutex
doc: document auto_init
uart0: remove superfluous prototype from header

Declare and document prototype in CPU part instead.
doc: document board_uart0 module
cc110x: cleanup cc110x_legacy_csma driver

Remove unused radio_t struct and fixed documentation.
doc: fix doxygen warnings for CBOR
cbor: fixe line length
doc: cbor: complemented documentation
doc: fixed documentation for transceiver
doc: added missing documentation for PRIu32
doc: fix vtimer documentation
doc: avr cleanup
doc: fix bloom filter documentation
doc: fix quat_math documentation
doc: fix posix wrapper documentation
doc: fixed documentation for crypto headers
Merge pull request #2149 from OlegHahm/doxygen_sys_cleanup

doc: doxygen sys cleanup