Remove uhdm libs out of own folder, use soversion (fixes #992)

[timkpaine]

This PR does two things:

• instead of installing into lib/uhdm/, we will install into lib. This is the normal method, installing into lib/uhdm/ has caused problems on both conda and homebrew, and is sure to continue to cause headaches
• we use SOVERSION so that lib/libuhdm.so is now a symlink, and we install a versioned lib/libuhdm.so.<major>.<minor>

Fixes #992

(I will do a similar PR for Surelog)

---

-- Installing: /tmp/uhdm-install/lib/libuhdm.so.1.71
-- Installing: /tmp/uhdm-install/lib/libuhdm.so

[alaindargelas]

@hzeller please review early next week.

[mithro]

@hzeller is out of office until 28th August

[timkpaine]

there's no explicit rush (other than the desire to not leave PRs open for too long).