Miscellaneous clean up of Rust bindings

[jbangelo]

Just a few odds and ends that I felt should be cleaned up. Already split up into logical commits if you prefer.

1. Added a few "keywords" to the Cargo.toml
2. Fixed a crash in the parser caused when the buffer ran out of data and didn't get refilled
3. Added a very bare bones description of the crate for the doc generation
4. Added a more formally defined Result and Error type for the crate to use

[silverjam]

LGTM in general, added a few comment though

[benjaminaltieri]

I got this warning when compiling using make test-rust, with rustc==1.3.8:

warning: trait objects without an explicit `dyn` are deprecated
warning: trait objects without an explicit `dyn` are deprecated
   --> src/parser/mod.rs:134:30
    |
134 | pub fn read_string(buf: &mut Read) -> Result<String, ::Error> {
    |                              ^^^^ help: use `dyn`: `dyn Read`
    |
    = note: `#[warn(bare_trait_objects)]` on by default

   --> src/parser/mod.rs:134:30
    |
134 | pub fn read_string(buf: &mut Read) -> Result<String, ::Error> {
    |                              ^^^^ help: use `dyn`: `dyn Read`
    |
    = note: `#[warn(bare_trait_objects)]` on by default

warning: trait objects without an explicit `dyn` are deprecated
   --> src/parser/mod.rs:140:36
    |
140 | pub fn read_string_limit(buf: &mut Read, n: u64) -> Result<String, ::Error> {
    |                                    ^^^^ help: use `dyn`: `dyn Read`

warning: trait objects without an explicit `dyn` are deprecated
   --> src/parser/mod.rs:140:36
    |
140 | pub fn read_string_limit(buf: &mut Read, n: u64) -> Result<String, ::Error> {
    |                                    ^^^^ help: use `dyn`: `dyn Read`

Worth addressing?

[jbangelo]

@benjaminaltieri I think you're on the wrong branch? The dyn has already been added there.