Adding Documentation on Hugo Template Functions

docs/content/layout/functions.md

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+---
+title: "Template Functions"
+date: "2013-07-01"
+linktitle: "Template Functions"
+groups: ["layout"]
+groups_weight: 70
+---
+
+Hugo uses the excellent golang html/template library for its template engine.
+It is an extremely lightweight engine that provides a very small amount of
+logic. In our experience that it is just the right amount of logic to be able
+to create a good static website.
+
+Go templates are lightweight but extensible. Hugo has added the following
+functions to the basic template logic.
+
+Golang documentation for the built-in functions can be found [here](http://golang.org/pkg/text/template/)
+
+## General
+
+### isset
+Return true if the parameter is set.
+Takes either a slice, array or channel and an index or a map and a key as input.
+
+eg. {{ if isset .Params "project_url" }} {{ index .Params "project_url" }}{{ end }}
+
+### echoParam
+If parameter is set, then echo it.
+
+eg. {{echoParam .Params "project_url" }}
+
+### first
+Slices an array to only the first X elements.
+
+eg.
+    {{ range first 10 .Data.Pages }}
+        {{ .Render "summary"}}
+    {{ end }}
+
+
+## Math
+
+### add
+Adds two integers.
+
+eg {{add 1 2}} -> 3
+
+### sub
+Subtracts two integers.
+
+eg {{sub 3 2}} -> 1
+
+### div
+Divides two integers.
+
+eg {{div 6 3}} -> 2
+
+### mul
+Multiplies two integers.
+
+eg {{mul 2 3}} -> 6
+
+### mod
+Modulus of two integers.
+
+eg {{mod 15 3}} -> 0
+
+### modBool
+Boolean of modulus of two integers.
+true if modulus is 0.
+
+eg {{modBool 15 3}} -> true
+
+## Strings
+
+### urlize
+Takes a string and sanitizes it for usage in urls, converts spaces to "-".
+
+eg. <a href="/tags/{{ . | urlize }}">{{ . }}</a>
+
+### safeHtml
+Declares the provided string as "safe" so go templates will not filter it.
+
+eg. {{ .Params.CopyrightHTML | safeHtml }}
+
+### lower
+Convert all characters in string to lowercase.
+
+eg {{lower "BatMan"}} -> "batman"
+
+### upper
+Convert all characters in string to uppercase.
+
+eg {{upper "BatMan"}} -> "BATMAN"
+
+### title
+Convert all characters in string to titlecase.
+
+eg {{title "BatMan"}} -> "Batman"
+
+### highlight
+Take a string of code and a language, uses pygments to return the syntax
+highlighted code in html. Used in the [highlight shortcode](/extras/highlight).