Resolve "Generated virtualenv should be removed when using `ninja clean`"

Closes #6

See merge request !6

Resolve "Invalid initializer in `declare_group` when processing a list of options"

Closes #5

See merge request !5

Resolve "Option keywords missing namespace if no converter is defined"

Closes #4

See merge request !4

Resolve "Change default filename for configuration file to `genopts.yml`"

Closes #3

See merge request !3

Resolve "Namespaces for keywords not honored when generating options"

Closes #2

See merge request !2

Resolve "Option converters not properly handled if not defined"

Closes #1

See merge request !1