support string functions

[fiji-flo]

• [x] abbrev: Truncate a string with ellipses. abbrev 5 "hello world" yields "he..."
• [x] abbrevboth: Abbreviate from both sides, yielding "...lo wo..."
• [x] trunc: Truncate a string (no suffix). trunc 5 "Hello World" yields "hello".
• [x] trim: strings.TrimSpace
• [x] trimAll: strings.Trim, but with the argument order reversed trimAll "$" "$5.00" or "$5.00 | trimAll "$"
• [x] trimSuffix: strings.TrimSuffix, but with the argument order reversed: trimSuffix "-" "ends-with-"
• [x] trimPrefix: strings.TrimPrefix, but with the argument order reversed trimPrefix "$" "$5"
• [x] upper: strings.ToUpper
• [x] lower: strings.ToLower
• [x] nospace: Remove all space characters from a string. nospace "h e l l o" becomes "hello"
• [ ] title: strings.Title
• [x] untitle: Remove title casing
• [x] repeat: strings.Repeat, but with the arguments switched: repeat count str. (This simplifies common pipelines)
• [x] substr: Given string, start, and length, return a substr.
• [x] initials: Given a multi-word string, return the initials. initials "Matt Butcher" returns "MB"
• [x] randAlphaNum: Given a length, generate a random alphanumeric sequence
• [x] randAlpha: Given a length, generate an alphabetic string
• [x] randAscii: Given a length, generate a random ASCII string (symbols included)
• [x] randNumeric: Given a length, generate a string of digits.
• [ ] swapcase: SwapCase swaps the case of a string using a word based algorithm. see https://godoc.org/github.com/Masterminds/goutils#SwapCase
• [ ] shuffle: Shuffle randomizes runes in a string and returns the result. It uses default random source in math/rand
• [ ] snakecase: convert all upper case characters in a string to underscore format.
• [ ] camelcase: convert all lower case characters behind underscores to upper case character
• [ ] wrap: Force a line wrap at the given width. wrap 80 "imagine a longer string"
• [ ] wrapWith: Wrap a line at the given length, but using 'sep' instead of a newline. wrapWith 50, "<br>", $html
• [x] contains: strings.Contains, but with the arguments switched: contains substr str. (This simplifies common pipelines)
• [x] hasPrefix: strings.hasPrefix, but with the arguments switched
• [x] hasSuffix: strings.hasSuffix, but with the arguments switched
• [ ] quote: Wrap string(s) in double quotation marks, escape the contents by adding '\' before '"'.
• [ ] squote: Wrap string(s) in double quotation marks, does not escape content.
• [ ] cat: Concatenate strings, separating them by spaces. cat $a $b $c.
• [x] indent: Indent a string using space characters. indent 4 "foo\nbar" produces " foo\n bar"
• [x] nindent: Indent a string using space characters and prepend a new line. indent 4 "foo\nbar" produces "\n foo\n bar"
• [x] replace: Replace an old with a new in a string: $name | replace " " "-"
• [x] plural: Choose singular or plural based on length: len $fish | plural "one anchovy" "many anchovies"
• [ ] sha256sum: Generate a hex encoded sha256 hash of the input