BUG/COMPAT: pickled dtindex with freq raises AttributeError in normalize related ops
BUG: reset_index with MultiIndex contains PeriodIndex raises ValueError
fix length of underlinings.
DOC: added nanosecond frequencies to doc
Docs: Be more specific about inf/-inf no longer being treated as nulls.
Merge pull request #7804 from sinhrks/nanodoc

DOC: added nanosecond frequencies to doc
Merge pull request #7800 from lexual/indexing_docs_structure_fix

Correct docs structure in indexing docs.
Merge pull request #7789 from sinhrks/normalize_pickle

BUG/COMPAT: pickled dtindex with freq raises AttributeError in normalize...
Merge pull request #7805 from lexual/docs_inf_as_null_note

Docs: Be more specific about inf/-inf no longer being treated as nulls.
Merge pull request #7802 from sinhrks/reset_index_bug

BUG: reset_index with MultiIndex contains PeriodIndex raises ValueError