Fix all errors in UG and amended DG

[LHeng1]

Closes #123

This PR amends both the UG and DG.

UG:

• Grammatical errors
• Formatting errors
• Full stops
• Checked expected output and error messages
• Scrolled through every single "
  " to find the one missing closer
• Some of the prefixes were missing
• Signs of addressbook

DG:

• Realized that Interview Score also can accept more than 2dp so added in the planned enhancements part

[codecov]

Codecov Report

Merging #211 (b890f94) into master (5e500f6) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #211   +/-   ##
=========================================
  Coverage     74.65%   74.65%           
  Complexity      666      666           
=========================================
  Files           107      107           
  Lines          2371     2371           
  Branches        247      247           
=========================================
  Hits           1770     1770           
  Misses          515      515           
  Partials         86       86           

[ravern]

LGTM