Jiffy 0.14.8

Jiffy 0.14.7

* Add double-conversion license to main LICENSE file

Jiffy 0.14.6

* Publish Jiffy on hex.pm

Jiffy 0.14.5

* Fix memory leak when encoding map terms
* Remove debug logging

Jiffy 0.14.4

* Fix dialyzer spec for jiffy:encode/1,2
* Fix compilation on GNU/Hurd

Don't rely on an environment variable for Travis

The environment variable approach breaks other projects' Travis-CI runs
if they include other projects that depend on a different version of
PropEr.

Fixes: davisp#106

Fix compiler warning on gcc 5.1.0

Add latest Erlang VMs to the test matrix

Fix dialyzer type specs

Account for char possibly being unsigned

This sounds rather insane to me but I've managed to show that `(char)
-1` is converted to 255 on some platforms. This was reproduced on
ppc64el via Qemu on OS X. A simple program that does `fprintf(stderr,
"%d\r\n", (char) -1);` prints 255 to the console. Rather than rely on
the signedness of a char I've just updated things to use an unsigned
char (which hopefully is never signed) and replaced -1 with 255 for the
sentinel value when converting hex values.

Thanks to Balint Reczey (@rbalint) for the report.

Fixes davisp#74