As we are going to publish the crate to crates.io, we need a different
name and version. Since native library is upgraded, all versions are
bumpped to 0.4.0. To make it clear which version of jemalloc is used, I
attach a build tag 5.2.1.
And the project are upgraded to 2018 version.
Signed-off-by: Jay Lee <BusyJayLee@gmail.com>