Merge pull request #12 from mgage/master

update instructions for location of OPL
Corrected typo in DBSection tag.
Fixed section tags.
Added Holt Linear Algebra to Textbook file, updated a problem tag.
Fixed tags.
Fixed tags.
Modified tags.
Updated tags in linear algebra problems, and fixed a few typos.
Whitespace change -- look nicer and testing
Fix tags
Fixed tags.
Added Holt Linear Algebra text tags and fixed a few typos.
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
Fix tags
Added end of line on last line
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
Added beginproblem
Fix issue with parsing a scalar into thousands digits and hundreds digits

Use substr($y,-6,3) and substr($y,-3,3) to get the thousands digits and hundreds digits of numbers.
Add clarifying instructions to problem text

(Use at least four decimal places in any constants
in your answer.)