Log Message:
Update to 0.9.1

Changelog:
## 0.9.1
     * Various improvements to comment output. \ 
https://github.com/eqrion/cbindgen/pull/370 / \ 
https://github.com/eqrion/cbindgen/pull/375.
     * Fixed expand when ran from build.rs. \ 
https://github.com/eqrion/cbindgen/pull/371
     * More debugging output for expansion. \ 
https://github.com/eqrion/cbindgen/pull/383
     * New option to add a default private constructor in C++ tagged enums. \ 
https://github.com/eqrion/cbindgen/pull/377
     * Syn and related dependencies updated to 1.0. \ 
https://github.com/eqrion/cbindgen/pull/379