Rewrite feature list to comply with convention

[yadobler]

standardise PREFIX flags:

• t/ and p/ used in multiple places, causing collision
• need to make a list somewhere

follow format for examples

Command REQ_ARG1 REQ_ARG2+ [OPT_ARG] [OPT_ARG]*

Where:

• Command is the command verb
• REQ_ARG is the required argument(s)
• [OPT_ARG] is the optional argument(s)

use the following Kleene operator suffix / number brackets to denote number arguments:

• nothing for:
  • exactly 1 argument (REQ_ARG)
  • 0 or 1 arguments (OPT_ARG) (implicit ?)
• * for {0..infinite} for OPT_ARG
• {x..y} for minimum of x maximum of y
  • OPT_ARG must be {0..y} else it isn't optional
• for functions that accept one or more of a certain argument, either
  1. + for {1..infinite} for REQ_ARG
  2. Have a single REQ_ARG and then another [OPT_ARG]*for additional

Eg:

add n/NAME p/PHONE_NUMBER e/EMAIL a/ADDRESS [t/TAG]*

Either one

find KEYWORD [MORE_KEYWORDS]*

Or

find KEYWORD+