Release 1.2-alpha

This is an alpha release with many improvements, including:
- Speech quality improvements especially in the 12-20 kbit/s range
- Improved VBR encoding for hybrid mode
- More aggressive use of wider speech bandwidth, including fullband speech
    starting at 14 kbit/s
- Music quality improvements in the 32-48 kb/s range
- Generic and SSE CELT optimizations
- Support for directly encoding packets up to 120 ms
- DTX support for CELT mode
- SILK CBR improvements
- Support for all of the fixes in draft-ietf-codec-opus-update-04 (the mono
    downmix and the folding fixes need --enable-update-draft)
- Many bug fixes, including integer overflows discovered through fuzzing
    (no security implications)
This tag has no release notes.