allow uaddr() to work on non-bash

fix 64-bit integer constants

Tools

add apt.llvm.org apt-key instructions needed for newer/secured Ubuntu

Uaddr

Doc updates

Show Clang warnings and fix warnings we were causing with missing semicolons

usdt: fix attaching to USDT on Bionic Beaver

fix hist() bars

add kaddr() cal

bpftrace was using an approach different from bcc to calculate the
offset of an USDT probe. We were using only `bcc_usdt_get_location`,
whereas bcc is using a combination of `bcc_usdt_get_location` and
`bcc_resolve_symname`. Since we already use `bcc_resolve_symname` in
`AttachedProbe::offset()`, we just need to call this method to get the
same behavior from bcc.

Fixes: https://github.com/iovisor/bpftrace/issues/60

update docs to work past kprobe:sys_ changes