Improve speed of SG_*IO debug functions

- SG_DEBUG & co are likely not enabled. Improve macros to test if
loglevel is above the to-be-shown level and only then call io code
- Note: This change requires that all SG_*IO functions no longer have a
trailing ";", e.g. SG_DEBUG("hi there...") is sufficient.
remove legacy whitespace in all SG_*IO functions

like SG_INFO( "foo") -> SG_INFO("foo")
Fix a couple of clang compiler warnings.
enable more strict compiler settings
Disabled optimizations in travis
really disable optimizations in travis
remove cstring include to hopefully fix clang compile error
fix some clang compile errors
Removed unused covertree
Removed duplicate of fibonacci heap
Removed unused arpack wrapper and removed unused covertree import
mention perl interface and data in README
-finally make median kernel selection work
-bugfixed (added a new constructor to SGMatrix)
-added a new test for median kernel selection
Merge pull request #858 from karlnapf/master

Finally finished all mmd kernel selection methods
fix (harmless) error messages on make install

better avoid them to not confuse us users or devlopers :)