Travis changes

• Modernise the Travis incantations, which have become old and faded since they were first written
• Specify a MSRV (1.42.0) and compile on more architectures
• Test the power set of features on Stable

.travis.yml

@@ -1,13 +1,19 @@
-before_install:
-  - sudo add-apt-repository --yes ppa:kubuntu-ppa/backports
-  - sudo apt-get update -qq
-  - sudo apt-get install cmake
-sudo: true
 language: rust
 rust:
+  - 1.42.0
   - stable
-script:
-    - cargo build --verbose
-    - cargo test  --verbose
-    - cargo build --verbose --no-default-features
-    - cargo test  --verbose --no-default-features
+  - beta
+  - nightly
+
+jobs:
+  fast_finish: true
+  allow_failures:
+    - rust: nightly
+
+  include:
+    - name: 'Rust: test with all features'
+      rust: stable
+      install:
+        - cargo install cargo-hack
+      script:
+        - cargo hack test --feature-powerset