Switch CI support from Travis to GitHub Actions (#8)

Created .github/workflows/ci.yml; iterated to figure out how to properly run the tests and upload coverage to Codecov. Updated README badges.

Author: MilosAtz

.github/workflows/ci.yml

@@ -0,0 +1,60 @@
+name: CI
+
+on:
+# Triggers the workflow on push or pull request events for the master/develop branches
+  push:
+    branches:
+      - master
+      - develop
+  pull_request:
+    branches:
+      - master
+      - develop
+  # Allows us to run this workflow manually
+  workflow_dispatch:
+
+jobs:
+  main:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        python-version: [3.8, 3.7, 3.6]
+   
+    name: "Python ${{ matrix.python-version }}"
+    steps:
+      - uses: actions/checkout@v2
+      
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+          
+      - name: Package setup
+        shell: bash
+        run: |
+          pip install -r requirements.txt
+          pip install .
+      
+      - name: Package tests
+        shell: bash
+        run: pytest --cov=./dassh ./tests/ --cov-report xml:coverage_${{ matrix.python-version }}.xml
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v2
+        with:
+          fail_ci_if_error: true
+          flags: unittests
+          name: codecov-umbrella
+          verbose: true
+          files: coverage_${{ matrix.python-version }}.xml
+          # dry_run: true
+
+  #finish:
+  #  needs: main
+  #  runs-on: ubuntu-latest
+  #  steps:
+  #    - name: CodeCov
+  #      shell: bash
+  #      run: codecov
+    

.travis.yml

@@ -1,7 +1,7 @@
 # Ducted Assembly Steady State Heat Transfer Software (DASSH)
 
-[![Build Status](https://travis-ci.com/dassh-dev/dassh.svg?token=9JiRbxest2oH9X8ijsPq&branch=master)](https://travis-ci.com/github/dassh-dev/dassh)
-[![codecov](https://codecov.io/gh/dassh-dev/dassh/branch/master/graph/badge.svg)](https://app.codecov.io/gh/dassh-dev/dassh)
+[![Build](https://github.com/github/docs/actions/workflows/ci.yml/badge.svg?branch=develop)
+[![codecov](https://codecov.io/gh/dassh-dev/dassh/branch/develop/graph/badge.svg)](https://app.codecov.io/gh/dassh-dev/dassh)
 [![License](https://img.shields.io/badge/License-BSD%203--Clause-blue.svg)](https://opensource.org/licenses/BSD-3-Clause)