Remove max_versioned_symbol, fix version policy check

[ehashman]

Hopefully fixes #41 (and definitely #42).

[njsmith]

Noting for the record, the main change here is that instead of trying to parse the version strings to convert them into sortable numbers -- which is sorta unfortunate since they're really arbitrary tokens -- this changes the policy to just have a list of which version string tokens are allowed. This makes things simpler and more correct.

[ehashman]

For the record, sketchy way I used to generate the list of versions on the manylinux docker:

(in manylinux docker with libs from lib_whitelist)# for lib in "libpanelw.so.5" "libncursesw.so.5" "libgcc_s.so.1" "libstdc++.so.6" "libm.so.6" "libdl.so.2" "librt.so.1" "libcrypt.so.1" "libc.so.6" "libnsl.so.1" "libutil.so.1" "libpthread.so.0" "libX11.so.6" "libXext.so.6" "libXrender.so.1" "libICE.so.6" "libSM.so.6" "libGL.so.1" "libgobject-2.0.so.0" "libgthread-2.0.so.0" "libglib-2.0.so.0"; do readelf -V `ldconfig -p | grep $lib | sed 's|.*=> ||'` >> /versions.txt; done

$ docker cp silly_hamilton:/versions.txt symbols.txt
$ vim symbols.txt
<removed any non-.gnu.version_d sections>
$ grep 'Name:' symbols.txt > symbols2.txt  # gets only lines with version names
$ grep -v 'Name: .*\.so' symbols2.txt | awk '{ print $11 }' | sort -u  # removes version names corresponding to .so's