Build RTS as shared library

The C RTS is now built as a shared library, so that the functions in the Idris
standard library that use parts of it will work in :x and in type providers.
Statically link to RTS in generated C code
Basically working executor/interpreter
Documentation improvement
Remove debug tracing
Add test for sequencing of I/O in executor
Remove debugging help
Improve FFI accuracy in executor
Fix expected output for test024
OS detection in config.mk without using uname

GCC has an option -dumpmachine which provides the necessary info.
Use just-built dynamic RTS during library typecheck

Idris has been extended with a flag to choose which dynamic RTS library will
be loaded on startup. The build system has been updated to build the dynamic
RTS after Idris but before typechecking the stdlib. Typechecking the stdlib
now uses the just-build dynmic RTS in dist/.
Added new tests to the test README
Build fat RTS lib on OS X
Fix "make relib" to use dynamic rts
Force gcc to use the same architecture as ghc on Mac OS X
An effect to allocate and manipulate memory
Test fixed
Made do_poke private
Update type providers so that the decision of failure or otherwise is made in IO
Add support for pointers to dynamic FFI