Protect the streams list of MediaInfoWrapper with a mutex.

We recently switched to creating MediaInfo instances multiple times and
simultaneously, and got rid of these instances more often. Under some
circumstances we have experienced segmentation faults in the MediaInfoNative
synchronization implementation, specifically in the BaseStream destructor
and the MediaInfoWrapper destructor, which both operate on the (not thread-safe)
STL list `streams`.

```
/lib64/libpthread.so.0(+0x331660f710) [0x7f478937d710]
mediainfo_native.so(_ZNSt14_List_iteratorIPN15MediaInfoNative10BaseStreamEEppEv+0xf) [0x7f471b82bf39] client.c:764
mediainfo_native.so(_ZNSt4listIPN15MediaInfoNative10BaseStreamESaIS2_EE6removeERKS2_+0x4e) [0x7f471b82bfd4] client.c:783
mediainfo_native.so(_ZN15MediaInfoNative16MediaInfoWrapper25notifyOfStreamDestructionEPNS_10BaseStreamE+0x27) [0x7f471b82b967] client.c:585
mediainfo_native.so(_ZN15MediaInfoNative10BaseStreamD2Ev+0x30) [0x7f471b829c1a]
mediainfo_native.so(+0x39fe) [0x7f471b8299fe]
```

It looks like Ruby threads the garbage collector now, at least the destructors
seem to be called in parallel.

This patch adds a pthread mutex around the `streams` container and should prevent
these (rare) segmentation faults.
Bump to 0.1.1.
Merge branch 'release/0.1.1' into develop