Many updates/fixes to 2018/burton2

This is a big commit but it should complete this entry and 2018 unless I
have missed something.

The make test rule was fixed. A script was not +x.

Renamed freqcount -> freqcount.sh (for browser/display).

Renamed mkkeywords -> mkkeywords.sh (for browser/display).

Renamed runtest -> runtest.sh (for browser/display).

Renamed spotcheck -> spotcheck.sh (for browser/display).

Renamed spotdiff -> spotdiff.sh (for browser/display).

Made tac.man proper man format and renamed tac.1.

Added tokcount.sh - a script that the author included in the remarks but
not in a script.

The renaming of files should be okay including the manifest (it is
believed this is true anyway).

Add try.sh script.

The READ_ME.txt was deleted as it had been renamed to author-README.txt
but the former was never deleted. This file was typo/format checked.

Format/typo check README.md file.

2018/burton2/tac.c

@@ -37,7 +37,7 @@ awk '/^[^$]/{l=length;m=m>l?m:l;a[l]=a[l]$1}
  * 
  * DO NOT EDIT the string kw; instead:
  *
- *	mkkeywords < my.list > my.keywords
+ *	mkkeywords.sh < my.list > my.keywords
  *	cc -DW=\"my.keywords\" -o tac tac.c
  */