Add go.mod, update CI and badges

.github/workflows/build.yml

@@ -0,0 +1,25 @@
+name: Build
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+
+    - name: Set up Go 1.x
+      uses: actions/setup-go@v2
+      with:
+        go-version: ^1.15
+
+    - name: Check out code into the Go module directory
+      uses: actions/checkout@v2
+
+    - name: Test
+      run: go test -v -cover .

README.md

@@ -1,6 +1,6 @@
 # piecewiselinear
 
-[![](https://godoc.org/github.com/sgreben/piecewiselinear?status.svg)](http://godoc.org/github.com/sgreben/piecewiselinear) [![](https://goreportcard.com/badge/github.com/sgreben/piecewiselinear/goreportcard)](https://goreportcard.com/report/github.com/sgreben/piecewiselinear) [![coverage](http://gocover.io/_badge/github.com/sgreben/piecewiselinear)](https://gocover.io/github.com/sgreben/piecewiselinear) [![Build Status](https://travis-ci.org/sgreben/piecewiselinear.svg?branch=master)](https://travis-ci.org/sgreben/piecewiselinear)
+[![](https://godoc.org/github.com/sgreben/piecewiselinear?status.svg)](http://godoc.org/github.com/sgreben/piecewiselinear) [![](https://goreportcard.com/badge/github.com/sgreben/piecewiselinear/goreportcard)](https://goreportcard.com/report/github.com/sgreben/piecewiselinear) [![gocover.io](https://gocover.io/_badge/github.com/sgreben/piecewiselinear)](https://gocover.io/github.com/sgreben/piecewiselinear) [![Build](https://github.com/sgreben/piecewiselinear/workflows/Build/badge.svg)](https://github.com/sgreben/piecewiselinear/actions?query=workflow%3ABuild)
 
 A tiny library for linear interpolation. `O(log(N))` per evaluation for `N` control points.
 

go.mod

@@ -0,0 +1,3 @@
+module github.com/sgreben/piecewiselinear
+
+go 1.15