resolves #80: reverse-proxy with custom base URL

Fix all hrefs and vue routes to correctly operate against the
<base href> tag. Add a configuration parameter to override the
content of the href attribute, and describe its use.

etc/laminar.conf

@@ -43,6 +43,16 @@
 ###
 #LAMINAR_KEEP_RUNDIRS=0
 
+
+###
+### LAMINAR_BASE_URL
+###
+### Base url for the frontend. This affects the <base href> tag and needs
+### to be set if Laminar runs behind a reverse-proxy that hosts Laminar
+### within a subfolder (rather than at a subdomain root)
+###
+#LAMINAR_BASE_URL=/
+
 ###
 ### LAMINAR_ARCHIVE_URL
 ###