add errata markdown draft
change title
move errata file to an errata folder
rename file to include edition 1, printing 1
add errata for ch 18 and 21
add remainder of errata from forum errata board
add names to chapter sub-titles and include errata from my notes
remove out of data errata.txt file
Merge pull request #1 from bignerdranch/add-errata-markdown

add errata markdown draft