Early version of M-SSA. Somehow works...
Unbreak the usual SSA
Add lrr and rforecast (L-forecast) for mssa
First cut of complex SSA
Use proper number of eigenvalues for complex SSA
Speedup
Speedup hmat-building in `decompose.mssa.eigen'
Fix hmat-building in `decompose.mssa.svd'
Add support for unequal series lengths for MSSA. Along the lines:

1. Introduce new kind of "elementary series": series list. Overload the arithmetic ops on it
2. Streamline the hanlding of attributes
3. Get rid of .slength
4. Make sure the common methods do no decisions about e.g. contents
5. Cleanups here and there
Implement fixup for .apply.attributes
Add k-forecast
Get rid of executable flag
Document rforecast.mssa