Migrate Travis CI to GitHub actions CI (#85)

* Migrate CI from Travis to GitHub Actions

Replaces the Travis configuration with an equivalent GitHub Actions
workflow at .github/workflows/ci.yml. Same matrix (ubuntu-latest +
macos-latest), same build pipeline (autogen.sh, make, make check,
make install), same on-failure log dump for utils/*.log.

Two minor modernizations:
  - Switches the Ubuntu guile package from guile-2.0-dev to
    guile-3.0-dev. guile-2.0 was dropped from Ubuntu after 20.04;
    libctl already builds and runs against guile 3.0.
  - macOS dependency install adds autoconf/automake/libtool explicitly
    rather than relying on the runner image to provide them.

Workflow triggers on push to master, pull_request to master, and
manual workflow_dispatch. fail-fast disabled so a failure on one OS
doesn't cancel the other.

Also removes the Travis CI badge from README.md and replaces it with
a GitHub Actions badge pointing at the new workflow.

* CI: drop macOS, add OMP_NUM_THREADS matrix to exercise parallel tests

Drops the macos-latest matrix entry per maintainer preference (less
useful: project is primarily Linux-targeted, macOS runners cost more
minutes, and the existing Travis macOS coverage didn't exercise
anything Linux didn't).

Adds --enable-openmp to the configure step and matrices the run on
OMP_NUM_THREADS = 1 and 8. Both values share the same build; only
the runtime thread count differs. This catches regressions in the
parallel test paths (test-prism's #pragma omp parallel for loops in
test_point_inclusion, test_normal_to_object, and
test_line_segment_intersection) that a serial-only run wouldn't
flag — same matrix philosophy used to validate the prism
thread-safety work in PR #75 / #81.

Author: Luochenghuang

.github/workflows/ci.yml

@@ -0,0 +1,41 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+  workflow_dispatch:
+
+jobs:
+  build:
+    name: linux (OMP_NUM_THREADS=${{ matrix.omp_threads }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        omp_threads: [1, 8]
+    env:
+      OMP_NUM_THREADS: ${{ matrix.omp_threads }}
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y autoconf automake libtool guile-3.0-dev
+
+      - name: Build and test
+        run: |
+          sh autogen.sh --prefix=$PWD/.local --enable-openmp
+          make
+          make check
+          make install
+
+      - name: Print test logs on failure
+        if: failure()
+        run: |
+          for log in utils/*.log; do
+            [ -f "$log" ] && { echo "=== $log ==="; cat "$log"; }
+          done

.travis.yml

@@ -1,5 +1,5 @@
 [![Latest Docs](https://readthedocs.org/projects/pip/badge/?version=latest)](http://libctl.readthedocs.io/en/latest/)
-[![Build Status](https://travis-ci.org/NanoComp/libctl.svg?branch=master)](https://travis-ci.org/NanoComp/libctl)
+[![CI](https://github.com/NanoComp/libctl/actions/workflows/ci.yml/badge.svg)](https://github.com/NanoComp/libctl/actions/workflows/ci.yml)
 
 This is libctl, a [Guile](http://www.gnu.org/software/guile/)-based library for supporting flexible control
 files in scientific simulations.