Option parser

Supports keyword options that have a value, are a boolean flag, or enumeration types (string or int).

The software pattern is:

function(a, b, c, varargin)
opt.foo = false;
opt.bar = true;
opt.blah = [];
opt.choose = {'this', 'that', 'other'};
opt.select = {'#no', '#yes'};
opt = optparse(opt, varargin);

Optional arguments to the function behave as follows:
'foo' sets opt.foo <- true
'nobar' sets opt.foo <- false
'blah', 3 sets opt.blah <- 3
'blah', {x,y} sets opt.blah <- {x,y}
'that' sets opt.choose <- 'that'
'yes' sets opt.select <- 2 (the second element)

and can be given in any combination.

If neither of 'this', 'that' or 'other' are specified then opt.choose <- 'this'.

Alternatively if:
opt.choose = {[], 'this', 'that', 'other'};
then if neither of 'this', 'that' or 'other' are specified then opt.choose <- []

If neither of 'no' or 'yes' are specified then opt.select <- 1.

Note:
- That the enumerator names must be distinct from the field names.
- That only one value can be assigned to a field, if multiple values are required they must be converted to a cell array.
- To match an option that starts with a digit, prefix it with 'd_', so the field 'd_3d' matches the option '3d'.
The allowable options are specified by the names of the fields in the structure opt. By default if an option is given that is not a field of opt an error is declared.

Sometimes it is useful to collect the unassigned options and this can be achieved using a second output argument
[opt,arglist] = tb_optparse(opt, varargin);
which is a cell array of all unassigned arguments in the order given in varargin.