Make fax a default feature

[Shnatsel]

Fax was commonly requested, so let's make it Just Work when tiff crate is used through image where it's difficult to fiddle with tiff crate features.

[197g]

I'm not sure if it is ready as such, yet. I'm glad for using fax and it certainly does something non-trivial with a decent implementation; but it also uses a build-time syn=1 dependency for an internal derive feature. Before having it on as a default feature I'd like to ensure we're on a cleaner dependency tree—it's harder to turn off than on and in image we don't use an explicit feature list.

[Shnatsel]

All right. I've opened an issue upstream to upgrade to syn 2.x, but for now let's just go ahead and cut a release with fax support present but not enabled by default.

Never mind, we're still not handling photometric interpretation correctly: #229 (comment)

[Shnatsel]

fax v0.2.6 is now up with an upgrade to syn 2.x