Clean up vocabulary in browse

[bochocki]

Names should be more intuitive, adhere to the snake_case, and functions should adhere to object_verb() syntax.

We should use "vars" as often as possible (e.g., full_tbl --> all_vars)

Add more descriptive comments, especially to difficult/confusing lines that are currently uncommented.

[AldoCompagnoni]

Changed function to more intuitive names.
Objects whose name have changed
err_full_tab to vars_spell.
possible_args to possible_vars
possibleargs to possiblevars (in test_browse.R only)
sbst_popler to logic_expr
key_arg to keyword_subset
out_cols to out_vars
elastic_tab to nest_taxa
elastic_data to nested_data