Going over initial parts of the scripting overview.

I made a light pass over the text. Switched the includes over to the
new btest-include and adapted the other TEXT-EXECs a bit.

Also includes more tweaking all over the Sphinx setup.

testing/btest/doc/sphinx/include-scripts_base_init-bare_bro.btest

@@ -0,0 +1,7 @@
+# @TEST-EXEC: btest-diff %INPUT
+
+-- init-bare.bro
+
+type string_array: table[count] of string;
+type string_set: set[string];
+type addr_set: set[addr];