Demo packages for CPPAN

See some notable libraries below. All are prefixed with pvt.cppan.demo. Many of them were taken from master, so do not consider as stable!

1. boost 1.60.0 (not all libraries are tested)
2. boost experimental or new libs: fit, di, hana
3. sqlite3
4. gsl (should be microsoft.gsl)
5. google's protobuf, googletest, highwayhash
6. concepts libraries (can help you to try them easily): https://cppan.org/projects/pvt.cppan.demo.concepts
7. compression: zlib (1.2.8), bzip2 (1.0.6) - both stable versions.
8. image libs: png, gif, tiff, webp, leptonica
9. sqlpp11 libs and connectors - https://cppan.org/search?q=sqlpp11
10. libressl 2.3.2 - release version, but do not rely on it. Such libraries should be verified very good first. Maybe later an official version will come from its devs.
11. range-v3
12. mach7