Added some more decoder methods.

- Added some L1/sparse solvers
- decoder methods that solve for a weight matrix are now supported
Cleaned up decoder solvers and added tests.

- added allclose function, allows you to account for delays,
  exclude the beginning and end of signal, and do a plot.
- added filtfilt function for delay-free filtering.
Fixed some function imports re: new utils.
Updated conftest to skip benchmark tests.