[fix] Use `inttypes.h` macros
Fix Warning

Signed-off-by: Hrishikesh Dhayagude <dhrishi@marvell.com>
Merge pull request #62 from xively/correct_casting_of_feed_id_t

[fix] Correct casting of `feed_id_t`
[feature] new layer for non blocking architectures
[feature] added non blocking xively runners
[reafac][feature] changes to the way that io layer processes data

* added the non blocking version of functions
[build] made changes to Makefiles to make the non blocking compilation optional
[build] Update `update_mbed_repo` target
[fix][build] Revision variable name
[fix][mbed] Add missing `common.h`
[fix][mbed] Remove stale assertions
[fix][mbed] Remove stale `send_all()`
[fix][mbed] Add missing declarations
[mbed] Provide default setting for `XI_IO_LAYER` -

user may override this in `xi_user_config.h`, but they must know
what they are doing then!
[fix][mbed] Delete stale reference to `conn`
[fix][mbed] Fix compilation error
[fix] Typo that producess very odd compiler errors
[fix] Very trivial copypasta
[refac][fix] makes the library to use less stack memory
[refac] removed static text references