Use furo docs theme

This MR migrates the online documentation to use the furo theme which provides numerous improvements over sphinx_rtd_theme, in particular automatic dark mode themeing.

docs/conf.py

-# dqsegdb2 documentation build configuration file
+# gwdatafind documentation build configuration file
 
 import inspect
 import re
@@ -37,6 +37,7 @@ html_theme_options = {
     ],
 }
 
+# need fontawesome for the gitlab icon in the footer
 html_css_files = [
     "https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.1.2/css/fontawesome.min.css",
     "https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.1.2/css/solid.min.css",
@@ -92,6 +93,12 @@ napoleon_use_rtype = False
 def _project_git_ref(version, prefix="v"):
     """Returns the git reference for the given full release version.
     """
+    # handle builds in CI
+    if getenv("GITLAB_CI"):
+        return getenv("CI_COMMIT_REF")
+    if getenv("GITHUB_ACTIONS"):
+        return getenv("GITHUB_SHA")
+    # otherwise use the project metadata
     _setuptools_scm_version_regex = re.compile(
         r"\+g(\w+)(?:\Z|\.)",
     )
@@ -106,7 +113,7 @@ PROJECT_URL = getenv(
     "CI_PROJECT_URL",
     "https://git.ligo.org/computing/gwdatafind/client",
 )
-PROJECT_BLOB_URL = f"{PROJECT_URL}/-/blob/{PROJECT_GIT_REF}/{PROJECT_PATH.name}"
+PROJECT_BLOB_URL = f"{PROJECT_URL}/blob/{PROJECT_GIT_REF}/{PROJECT_PATH.name}"
 
 
 def linkcode_resolve(domain, info):