feat: modernize and expand cli (#4)

* refactor(base32): use new version;

* refactor(oath): replace oath with hmac and sha1;

* refactor(epoch): add epoch to calculation;

* feat(clap): use clap for parsing;

* feat(args): add interval as a cli arg;

I also reordered things.

* docs(cli): add docs to the cli via clap;

* feat(cli): add arg to set Unix time to start stepping form;

* feat(cli): add arg to specify number of digits in the output code;

* rm(bit mask): unneeded bit mask for conversions to sized ints;

* docs(cli): better docs and error messages;

* refactor(stdin): clean and rename stdin -> read_line_from_stdin;

* refactor(error): clean and rename error -> print_error_and_exit;

* feat(base32): automatically convert to uppercase;

* docs(cli): add extra note to interval doc comment;

* docs(README): update README.md to reflect new changes;