add missing documentation (lots!)

Here is the relevant output of `check()`:

```
> checking for missing documentation entries ... WARNING
Undocumented code objects:
‘FindFrozenTrials’ ‘FindLowData’ ‘RemoveFrozenTrials’ ‘RemoveLowData’
‘add_chi_noun_onset’ ‘all_basiclevel’ ‘all_errors’ ‘anonymous’
‘audio_cnames’ ‘binifyFixations’ ‘bl_types’ ‘blab_data’
‘cdi_get_words’ ‘cdi_words’ ‘characters_to_factors’
‘check_annot_codes’ ‘checkout_branch’ ‘checkout_commit’
‘chi_noun_onset’ ‘count_chi’ ‘count_chi_types’ ‘count_device_and_toy’
‘count_mot_fat’ ‘count_object_present’ ‘count_utterance’
‘expandFixList’ ‘fixations_report’ ‘get_df_file’
‘get_late_target_onset’ ‘get_mesrep’ ‘get_pairs’ ‘get_vocab_score’
‘get_windows’ ‘git_bin’ ‘home_dir’ ‘keypress_issues’
‘keypress_retrieved’ ‘late_target_retrieved’ ‘load_tsv’
‘malformed_speaker_codes’ ‘obj_pres’ ‘object2string’ ‘on_cdi’
‘outlier’ ‘reliability’ ‘rename_audio_header’ ‘rename_video_header’
‘string2object’ ‘subj_mos’ ‘subj_nums’ ‘subjectList’ ‘sync_repo’
‘sync_to_upstream’ ‘theme_AMERICA’ ‘theme_blab’ ‘theme_spooky’
‘utt_type’ ‘video_cnames’
All user-level objects in a package should have documentation entries.
See chapter ‘Writing R documentation files’ in the ‘Writing R
Extensions’ manual.
```