Remove Travis CI; Switch to Github Actions

Previous commits set up an initial install of github actions, this commit is
mostly removing Travis CI. Note that it does not completely remove Travis CI,
since our coverage job is not fully ported over yet. We do run the coverage job
in github actions, but don't upload it anywhere, currently. So for now, Travis
CI is still enabled, but only runs the coverage job and uploads the results to
coveralls.io.

.travis.yml

@@ -1,4 +1,4 @@
-sudo: false
+sudo: required
 
 language: rust
 cache:
@@ -7,15 +7,9 @@ cache:
 
 os:
 - linux
-- osx
-
-osx_image: xcode7.1
 
 rust:
-- 1.38.0
 - nightly
-- beta
-- stable
 
 addons:
   apt:
@@ -27,39 +21,6 @@ before_script:
 - echo PATH is $PATH
 - export RUST_BACKTRACE=1
 
-script: ./ci/script.sh
-
-env:
-  matrix:
-    - GIMLI_JOB="test"
-    - GIMLI_JOB="features"
-
-matrix:
-  fast_finish: true
-  include:
-    # Coverage should only run on Linux. tarpaulin currently requires nightly Rust.
-    - rust: nightly
-      os: linux
-      sudo: required
-      env: GIMLI_JOB="coverage"
-    # Building docs only needs to happen on one os and only on stable.
-    - rust: stable
-      os: linux
-      env: GIMLI_JOB="doc"
-    # Benching should only happen on nightly.
-    - rust: nightly
-      env: GIMLI_JOB="bench"
-    # Build a 32 bit target.
-    - rust: stable
-      sudo: required
-      services: docker
-      env:
-        - TARGET=i686-unknown-linux-gnu
-        - GIMLI_JOB=cross
-    # Build a big-endian target.
-    - rust: stable
-      sudo: required
-      services: docker
-      env:
-        - TARGET=powerpc64-unknown-linux-gnu
-        - GIMLI_JOB=cross
+script: |
+  RUSTFLAGS="--cfg procmacro2_semver_exempt" cargo install cargo-tarpaulin
+  cargo tarpaulin --verbose --ciserver travis-ci --coveralls "$TRAVIS_JOB_ID"

README.md

@@ -2,7 +2,7 @@
 
 [![](http://meritbadge.herokuapp.com/gimli) ![](https://img.shields.io/crates/d/gimli.svg)](https://crates.io/crates/gimli)
 [![](https://docs.rs/gimli/badge.svg)](https://docs.rs/gimli/)
-[![Build Status](https://travis-ci.org/gimli-rs/gimli.svg?branch=master)](https://travis-ci.org/gimli-rs/gimli)
+[![Build Status](https://github.com/fitzgen/peepmatic/workflows/Rust/badge.svg)](https://github.com/gimli-rs/gimli/actions)
 [![Coverage Status](https://coveralls.io/repos/github/gimli-rs/gimli/badge.svg?branch=master)](https://coveralls.io/github/gimli-rs/gimli?branch=master)
 
 `gimli` is a blazing fast library for consuming the