FIX: Documentation for for 0.14.1 change log

Missing code reference in change log documentation
BUG: unwanted conversions of timedelta dtypes when in a mixed datetimelike frame (GH7778)
TST: tests for internals/as_matrix() for all dtypes (including categoricals)
Merge pull request #7779 from jreback/td

BUG: unwanted conversions of timedelta dtypes when in a mixed datetimelike frame (GH7778)
Docs: Categorical docs fixups.
Merge pull request #7783 from lexual/docs_categorical_tidyup

Docs: Categorical docs fixups.
BUG: Bug in Series 0-division with a float and integer operand dtypes  (GH7785)
Merge pull request #7786 from jreback/div

BUG: Bug in Series 0-division with a float and integer operand dtypes  (GH7785)
Raise exception on non-unique column index in to_hdf for fixed format.

Fixes #7761.
TST: unicode compat for test_astype_unicode (GH7758)
BUG/COMPAT: pickled dtindex with freq raises AttributeError in normalize related ops
API: Add PeriodIndex.resolution
BUG: reset_index with MultiIndex contains PeriodIndex raises ValueError
fix length of underlinings.
BUG: is_superperiod and is_subperiod cannot handle higher freq than S
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.