Utility function to handle empty query results and templates (#1386)

* Add global Lua function 'some'

Moved documentation for 'each' function to non-standard section.

* Revert "Add optional argument to template.each for empty collection output (#1359)"

This reverts commit b73dadec67.

* Reimplement #1359 using 'some' function

common/space_lua/stdlib/global_test.lua

@@ -0,0 +1,27 @@
+local function assertEqual(a, b)
+    if a ~= b then
+        error("Assertion failed: " .. a .. " is not equal to " .. b)
+    end
+end
+
+-- Logic values, shouldn't be affected
+assertEqual(some(nil), nil)
+assertEqual(some(true), true)
+assertEqual(some(false), false)
+
+-- Numbers
+assertEqual(some(1), 1)
+assertEqual(some(0), 0) -- 0 is not falsy unlike C
+assertEqual(some(-1), -1)
+assertEqual(some(1/0), nil) -- inf
+assertEqual(some(0/0), nil) -- nan
+
+-- Strings
+assertEqual(some("foo bar"), "foo bar")
+assertEqual(some(""), nil)
+assertEqual(some(" \n"), nil)
+
+-- Tables
+assertEqual(some({}), nil)
+assertEqual(some({"baz"})[1], "baz") -- compare an element to ensure passthrough
+assertEqual(some({foo="bar"})["foo"], "bar")