Clean up ARPACK wrappers
Clean up bitarrays

- Remove redundant `return`s
- Collapse methods
- Return defined `Exception`s where appropriate
Clean up Hermitian matrix routines
Clean up generic matmuls

- Collapse loops using multiloop notation
- Remove redundant `return`s
Clean up sparse matrix routines
Clean up tridiagonal routines
Cleanup UMFPack routines

- Added `umferror()` error handler
Use meaningful `Exception` in `cov`