Optional case-insensitive literal comparison for strings (#9)

* More descriptive docs for path_or_nil and adding luacheck lints

* Have to run luarocks install separately for each package

* Adding more contributing docs

* Adding link to valid.lua

* Conistent function calling conventions in docs

* Adding allof and anyof validation functions

* Adding optional case-insensitive comparisons for string literals

* Consistent notes in readme

* Consistent notes in readme

* Adding more examples for comparing table literals

README.md

@@ -98,6 +98,10 @@ assert(is_valid)  -- true
 
 Validates that a value matches a specific literal.
 
+The comparison is performed using the equality operator (`==`), which means that both the value and the type must match exactly.
+
+Note: Two tables will not compare equal unless they are both references to *the same* table.
+
 #### Usage
 
 ```lua
@@ -108,8 +112,26 @@ assert(is_valid)  -- true
 
 local is_valid = valid.literal("abc")("123")
 assert(not is_valid)  -- false
+
+local is_valid = valid.literal("abc", {icase = true})("ABC")
+assert(is_valid)  -- true
+
+local price_table = {price = 1.00}
+
+local is_valid = valid.literal(price_table)({price = 1.00})
+assert(not is_valid) -- false, not the same table
+
+local is_valid = valid.literal(price_table)(price_table)
+assert(is_valid) -- true
 ```
 
+#### Parameters
+
+* `opts` (optional): Table of options.
+    * `icase`: Set to `true` to allow case-insensitive validation of a string literal.
+    * `func`: A custom validation function to call after the literal check.
+
+
 ### `valid.number`
 
 Validates that a value is a number within an optional range.

tests.lua

@@ -77,6 +77,18 @@ describe("Validation Library Tests", function()
     local simple_function = function() end
 
     local tests = {
+        {
+            description = "Case-insensitive literal",
+            definition = valid.literal("ALL CAPS", {icase = true}),
+            data = "all caps",
+            expected = {
+                is_valid = true,
+                val_or_err = "all caps",
+                badval_or_nil = nil,
+                path_or_nil = nil
+            }
+        },
+
         {
             description = "Valid string or number",
             definition = valid.anyof {valid.string(), valid.number()},

valid.lua

@@ -25,10 +25,17 @@ end
 
 local function literal(lit, opts)
     opts = opts or {}
+    local icase = opts.icase or false
     local func = opts.func or defaultfunc
 
     return function(val)
-        if val ~= lit then
+        if icase and type(lit) == "string" and type(val) == "string" then
+
+            if val:lower() ~= lit:lower() then
+                return false, "literal", val
+            end
+
+        elseif val ~= lit then
             return false, "literal", val
         end