Add a strict parsing feature (enabled by default)

[elrnv]

When enabled, strict will return an error when an obj contains a command that is not in the spec.

The motivation for this change is that obj is simple enough to allow others to easily extend it with domain specific commands. For instance the ARCsim cloth solver extends objs with face adjacency data.

It is beneficial for casual users and researchers to be able to parse such third party obj files.

[elrnv]

Sure! That sounds perfectly reasonable. Should we then start a LoadConfig struct like

struct LoadConfig {
    strict: bool
}

or just having a separate load_permissive calls or something like that?

[kvark]

Yes, let's have a LoadConfig struct