Document strings.TrimLeft and TrimRight template functions

Closes #147

content/functions/strings.TrimLeft.md

@@ -0,0 +1,28 @@
+---
+title: strings.TrimLeft
+description: Returns a slice of a given string with all leading characters contained in the cutset removed.
+godocref:
+date: 2017-02-01
+publishdate: 2017-02-01
+lastmod: 2017-02-01
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+keywords: [strings]
+signature: ["strings.TrimLeft CUTSET STRING"]
+workson: []
+hugoversion:
+relatedfuncs: [strings.TrimRight]
+deprecated: false
+aliases: []
+---
+
+Given the string `"abba"`, leading `"a"`'s can be removed a follows:
+
+    {{ strings.TrimLeft "abba" "a" }} → "bba"
+
+Numbers can be handled as well:
+
+    {{ strings.TrimLeft 1221 "12" }} → ""
+

content/functions/strings.TrimRight.md

@@ -0,0 +1,28 @@
+---
+title: strings.TrimRight
+description: Returns a slice of a given string with all trailing characters contained in the cutset removed.
+godocref:
+date: 2017-02-01
+publishdate: 2017-02-01
+lastmod: 2017-02-01
+categories: [functions]
+menu:
+  docs:
+    parent: "functions"
+keywords: [strings]
+signature: ["strings.TrimRight CUTSET STRING"]
+workson: []
+hugoversion:
+relatedfuncs: [strings.TrimRight]
+deprecated: false
+aliases: []
+---
+
+Given the string `"abba"`, trailing `"a"`'s can be removed a follows:
+
+    {{ strings.TrimRight "abba" "a" }} → "abb"
+
+Numbers can be handled as well:
+
+    {{ strings.TrimRight 1221 "12" }} → ""
+