Added "Define and operate on a type represented as a bitfield" example

[budziq]

I've added the bitflags example but unfortunately there is a linking error due to other book dependencies using different bitflags versions.

clap -> bitflags 0.8.2
png -> bitflags 0.7.0
openssl -> bitflags 0.9.1

This results in standard problem

error[E0465]: multiple rlib candidates for `bitflags` found
 --> /tmp/rust-skeptic.wsSHTSHfCBhF/test.rs:3:1
  |
3 | extern crate bitflags;
  | ^^^^^^^^^^^^^^^^^^^^^^
...

It the moment I have no idea how to work around such problem in general without changes to skeptic or cargo itself

fixes: https://github.com/brson/rust-cookbook/issues/189
fixes: https://github.com/brson/rust-cookbook/issues/114

---

• blocked on Update bitflags 0.8.0 -> 0.9 clap-rs/clap#966
• blocked on Update bitflags 0.7 -> 0.9 image-rs/image-png#56
• blocked on https://github.com/google/pulldown-cmark update to crates.io to 0.0.15
• blocked on https://github.com/brson/rust-skeptic/pull/32

Update: image-png and image have released a new version compatible with bitflags "^0.9". Still waiting for clap-rs dependencies updated on crates.io
Update: both image-png, image and clap-rs updated on crates.io but now we are still blocked on pulldown-cmark (skeptic transitive dependency).

[brson]

Seems like the root bug in skeptic needs to be fixed https://github.com/brson/rust-skeptic/issues/18. This is a horrible problem.

[budziq]

The https://github.com/brson/rust-skeptic/issues/18 will have to be solved otherwise contribution to and maintenance of cookbook will not be realistic (see this issue history).