DOC/BLD: Log errors in executed cells.
DOC/BLD: Add make notebook
Merge pull request #1470 from jseabold/nbgenerate-exceptions

DOC/BLD: Log code exceptions from nbgenerate
DOC: Fix import
Merge pull request #1471 from jseabold/fix-example-import

DOC: Fix import
DOC: Better header.
ENH: using human-readable group names instead of integer ids in MultiComparison
DOC: Add plots to the filters docs.
Merge pull request #1474 from jseabold/filter-plots

DOC: Add plots for standard filter methods.
added file that got left behind
Put back an import that my IDE incorrectly flagged as unused
ENH: Add weekly co2 dataset
DOC: Add new co2 dataset to release notes
Merge pull request #1481 from jseabold/co2-data

ENH: Add weekly co2 dataset
REF: Prefer filters.api to __init__
Merge pull request #1482 from jseabold/filter-api

REF: Prefer filters.api to __init__
ENH: Add freq_to_period function
REF: Add is_datetime_index function.
Merge pull request #1483 from jseabold/tsa-tools

ENH: Some utility functions for working with dates
BLD: New R versions require NAMESPACE file. Closes #1497.