manual: s/Polling Send/Non-Blocking Send

Clearer terminology

manual: Added <docref> XML Tag to Doxygen

Introduced a new Doxygen XML tag '<docref>'. The intention of
this tag is to indicate a section of text in the Doxygen XML that
will contain a reference to another section in the Manual e.g.
"See \autoref<sec:x>". As other generation formats aren't aware of
other chapters/sections in the manual, the <docref> encapsulation
allows it to omit the text from the output. The Latex generator
has been modified to continue parsing the 'docref' contents.

Fix: Guard seL4_DebugDumpScheduler with PRINTING instead of DEBUG

Definitions of seL4_DebugDumpScheduler (for each arch) guard
seL4_DebugDumpScheduler with PRINTING and not DEBUG.

manual: Expand parts of the x86 virtualisation documentation

This provides documentation for kernel design of the x86 virtualisation, the additional
syscall and object invocations. The ARM design is not fully expanded.

manual: allow non sec autorefs

Previously anything in an autoref block was assumed to reference
a section, which isn't true. Change 'sec' to 'label' and move the
'sec' prefix into the label itself.

libsel4: fix licenses

- some were incorrectly marked GPL (libsel4 is BSD)
- update NICTA --> DATA61 etc
- fix tags D61 --> DATA61
- update year to 2017

seL4_DebugDumpScheduler: add docs

SELFOUR-962: allow API level description in manual

manual: Add docs for seL4_Benchmark_FlushCaches

SELFOUR-961: allow lists in API docs

this change

- converts ordered doxygen lists to enumerate
- also wraps the benchmark config names in texttt

SELFOUR-910: document debugging syscalls

[SELFOUR-911]: Document benchmarking system calls

manual: Add missing return doc for seL4_Poll

manual: Docs for debugg and benchmark syscalls

libsel4: Optional public symbols for external interfaces

CONFIG_LIB_SEL4_PUBLIC_SYMBOLS=y will disable inlining for external
interfaces (except deprecated functions), thereby providing public
symbols for easy linkage with other languages.

Syscalls docs in manual generated by doxygen

This adds a dummy header with syscall prototypes with doxygen comments.
The build process for the manual includes parsing these comments using
doxygen. Doxygen produces an xml file which is parsed by a script to
generate latex which is included in the manual. This approach was chosen
over doxygen's native latex output to gain greater control over the
formatting of the generated documentation, and to take advantage of
existing api-formatting support in the sel4 manual.

Related issue: SELFOUR-606