Rustfmt updates + refactor Travis configuration (#60)

* Update rustfmt compliance

Looks like rustfmt has made some improvements recently, so wanted to bring the
code up to date.

* Add rustfmt to nightly item in Travis matrix

* Use Travis Cargo cache

* Allow fast_finish in Travis

Items that match the `allow_failures` predicate (right now, just Rust nightly),
will still finish, but Travis won't wait for them to report a result if the
other builds have already finished.

* Run kcov in a separate matrix build in Travis

* Rework allowed_failures logic

We don't want rustfmt to match `allow_failures` just because it needs to use
nightly, while we do want nightly to match `allow_failures`. Env vars provide a
solution.

* Add --all switch to rustfmt Travis

* Test building docs in Travis

* Use exact Ubuntu dependencies listed for kcov

Some of the dependencies we were installing were not listed on
https://github.com/SimonKagstrom/kcov/blob/master/INSTALL.md, and we were
missing one dependency that was listed there. When `sudo: true` Travis uses
Ubuntu Trusty.

* No need to build before running kcov

kcov builds its own test executables.

* Generate `Cargo.lock` w/ `cargo update` before running kcov

As noted in aeb3906cce8e3e26c7bc80d6aec417b365f3d2f1 it is not necessary to
build the project before running kcov, but kcov does require a `Cargo.lock`
file, which can be generated with `cargo update`.

.travis.yml

@@ -1,38 +1,50 @@
-
-sudo: required
-
 language: rust
+cache: cargo # https://docs.travis-ci.com/user/caching/#Rust-Cargo-cache
 
 rust:
   - stable
   - beta
-  - nightly
 
 matrix:
+  # Since this item is allowed to fail, don't wait for it's result to mark the
+  # build complete.
+  fast_finish: true
   allow_failures:
-    - rust: nightly
+    - env: NAME='nightly'
+    - env: NAME='kcov'
+  include:
+    - env: NAME='nightly'
+      rust: nightly
+    - env: NAME='rustfmt'
+      rust: nightly
+      before_script:
+        - rustup component add rustfmt-preview
+      script:
+        - cargo fmt --all -- --write-mode=diff
+    - env: NAME='kcov'
+      sudo: required # travis-ci/travis-ci#9061
+      before_script:
+        - cargo install cargo-update || echo "cargo-update already installed"
+        - cargo install cargo-kcov || echo "cargo-kcov already installed"
+        - cargo install-update -a
+      script:
+        - cargo kcov --print-install-kcov-sh | sh
+        - cargo update # Creates `Cargo.lock` needed by next command
+        - cargo kcov --verbose --features dss --coveralls -- --verify --exclude-pattern=/.cargo,/usr/lib,src/proto
+      addons:
+        apt:
+          packages:
+            - libcurl4-openssl-dev
+            - libdw-dev
+            - binutils-dev
+            - libiberty-dev
+            - zlib1g-dev
 
 env:
   global:
   - RUSTFLAGS="-C link-dead-code"
 
-addons:
-  apt:
-    packages:
-      - libcurl4-openssl-dev
-      - libdw-dev
-      - cmake
-      - g++
-      - pkg-config
-      - binutils-dev
-      - libiberty-dev
-
 script:
   - cargo build --verbose --all-features
   - cargo test --verbose --all-features
-
-after_success:
-  - cargo install cargo-kcov
-  - cargo kcov --print-install-kcov-sh | sh
-  - cargo kcov --verbose --features dss --coveralls -- --verify --exclude-pattern=/.cargo,/usr/lib,src/proto
-
+  - cargo doc --verbose --all-features