Adjust for recent change in mdds.
Change license from MIT to MPL 2.0.

Also add emacs and vim modelines.
Update for the license change.
Scripts to change licenses and add modelines in source files.
Support a way to append strings without checking for duplicates.

This is needed in case of duplicate strings one of which is unformatted
while the other has format runs. In xlsx these two are assigned different
string ID's.
Surround literal strings with double-quotes when printing formulas.
Forgot return statement here.
Remove compiler warnings.
Another compiler warning due to signed vs unsigned.
Bump the mdds version check to 0.9.0.
formula_parser to support different name resolver types.
Hide the name resolver concrete class.
rename formula_name_resolver_a1 -> excel_a1.

Short name now that it's just a hidden implementation detail.
Rename test name accordingly.
Skeleton name resolver for ODFF.
Make these methods inline, now that the whole class is hidden.
Handle single cell reference in ODFF.

Much of the code is a re-use of existing Excel A1 name resolver.
Some cleanup.
Use to_address() for this.
Handle range reference name resolution for ODFF.