.. value-table: in Xpress solver options

[fdabrandao]

In the current release of Xpress, solver options (https://dev.ampl.com/solvers/xpress/options.html) include .. value-table:. For instance:

alg:lpfolding (lpfolding)
      Simplex and barrier: whether to fold an LP problem before solving it:
      .. value-table:

[fdabrandao]

There are also some options that do not indicate possible values such as:

bar:alg (baralg)
      Which barrier algorithm to use

[glebbelov]

Fixed a few.