update doc for long long + size_t support
add doc specific to tfp_format
remove pointless test
moving tests to new test/ subdir
rename printf.* -> tinyprintf.*
allow to selectively compile-in printf/sprintf
test that tinyprintf compiles with various TINYPRINTF_* combinations
add snprintf/vsnprintf/vsprintf + tests

Note that these functions are supposed to return the number of chars
stored, this changes slightly the data structure they pass to
tfp_format.
set explicit C linkage
let gcc warn when printf params types don't match format

this moves the printf macro definition to the end of the header file,
otherwise the gcc __attribute__'s name ends up being 'tfp_format',
which is invalid.