Standardize GHA test setup, replace Travis badge with GHA (#232)

This brings the CI setup in line with the majority of Julia package
repositories. It's a mostly superficial change, though it also now
submits code coverage information to Codecov.

.github/workflows/ci.yml

@@ -0,0 +1,55 @@
+name: CI
+on:
+  push:
+    branches: [master]
+    tags: ["*"]
+  pull_request:
+jobs:
+  test:
+    name: Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }} - ${{ github.event_name }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        version:
+          - '1.1'
+          - '1'
+          - nightly
+        os:
+          - ubuntu-latest
+        arch:
+          - x64
+          - x86
+        include:
+          # test macOS and Windows with latest Julia only
+          - os: macOS-latest
+            arch: x64
+            version: 1
+          - os: windows-latest
+            arch: x64
+            version: 1
+          - os: windows-latest
+            arch: x86
+            version: 1
+    steps:
+      - uses: actions/checkout@v3
+      - uses: julia-actions/setup-julia@v1
+        with:
+          version: ${{ matrix.version }}
+          arch: ${{ matrix.arch }}
+      - uses: julia-actions/cache@v1
+      - uses: julia-actions/julia-buildpkg@v1
+      - uses: julia-actions/julia-runtest@v1
+      - uses: julia-actions/julia-processcoverage@v1
+      - uses: codecov/codecov-action@v3
+        with:
+          files: lcov.info
+  docs:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: julia-actions/julia-buildpkg@latest
+      - uses: julia-actions/julia-docdeploy@latest
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          DOCUMENTER_KEY: ${{ secrets.DOCUMENTER_KEY }}

README.md

@@ -3,7 +3,7 @@ LsqFit.jl
 
 The LsqFit package is a small library that provides basic least-squares fitting in pure Julia under an MIT license. The basic functionality was originally in [Optim.jl](https://github.com/JuliaNLSolvers/Optim.jl), before being separated into this library.  At this time, `LsqFit` only utilizes the Levenberg-Marquardt algorithm for non-linear fitting.
 
-[![Build Status](https://travis-ci.org/JuliaNLSolvers/LsqFit.jl.svg)](https://travis-ci.org/JuliaNLSolvers/LsqFit.jl)
+[![CI](https://github.com/JuliaNLSolvers/LsqFit.jl/actions/workflows/ci.yml/badge.svg)](https://github.com/JuliaNLSolvers/LsqFit.jl/actions/workflows/ci.yml)
 [![latest](https://img.shields.io/badge/docs-latest-blue.svg)](https://julianlsolvers.github.io/LsqFit.jl/latest/)
 
 Basic Usage