query: add --warn-exceptions, dateparser, docs (#290)

* query: add --warn-exceptions, dateparser, docs

added --warn-exceptions (like --raise-exceptions/--drop-exceptions, but
lets you pass a warn_func if you want to customize how the exceptions are
handled. By default this creates a logger in main and logs the exception

added dateparser as a fallback if its installed (it's not a strong dependency, but
I mentioned in the docs that it's useful for parsing dates/times)

added docs for query, and a few examples

--output gpx respects the --{drop,warn,raise}--exceptions flags, have
an example of that in the docs as well

.gitignore

@@ -12,6 +12,7 @@
 auto-save-list
 tramp
 .\#*
+*.gpx
 
 # Org-mode
 .org-id-locations