Types: Incoporate feedback from Steve Huston's review

Incorporate feedback from Steve Huston's review of the Types part (Part 1) of the document.

This JIRA covers small changes and minor corrections, typos, grammar and punctuation errors within the Types part (Part 1). In particular it is aimed at addressing the following points from Steve's mail(s):

Part 1, sect 1.1:
char "a single Unicode character"
uuid "a universally unique identifier as defined..."
string "a sequence of Unicode characters"

Part 1, sect 1.2, 1st para, last line "... within the application's
domain, and in messaging applications these custom types..." (remove ",
in" and comma after "applications")

Part 1, sect 1.2, 2nd para, Remove comma between "custom type" and "and".
3rd sentence: "... is actually a representation of the custom type" - do
not italicize.

Part 1, sect 2.2 Type: symbol. Should have a normative reference to ASCII.
American National Standard for Information Systems - Coded Character Sets

• 7-Bit American National Standard Code for Information Interchange (7-Bit
  ASCII), ANSI X3.4-1986, American National Standards Institute, Inc., March
  26, 1986

Part 1, sect 2.3, Type: map, 2nd para, 3rd sentence: replace dash between
"ordered" and that is", with a comma. Insert comma after "that is."

Part 1, sect 3, 1st para, 2nd sentence: "well-known" (insert hyphen
between "well" and "known").

Part 1, sect 3, 4th para, 4th (last) sentence: Replace "should be" with
"MUST".