dev-libs/tomsfastmath: New package

dev-libs/tomsfastmath: New package

"TomsFastMath is a fast public domain, open source, large integer
arithmetic library written in portable ISO C."

app-antivirus/clamav currently bundles this, and
the new dev-libs/libtomcrypto can optionally make
use of it.

Introduce it as a new package to keep track of security
issues.

Bug: https://bugs.gentoo.org/649394
Closes: https://bugs.gentoo.org/723856
Package-Manager: Portage-2.3.99, Repoman-2.3.22
Signed-off-by: Sam James (sam_c) <sam@cmpct.info>
Signed-off-by: Michael Orlitzky <mjo@gentoo.org>