Update humanize documentation (#27)

* update documentation to better detail expected functionality

* update tests to demonstrate internal capitalization

humanize.go

@@ -4,10 +4,14 @@ import (
 	"strings"
 )
 
-// Humanize returns first letter of sentence capitalized
+// Humanize returns first letter of sentence capitalized.
+// Common acronyms are capitalized as well.
+// Other capital letters in string are left as provided.
 // employee_salary = Employee salary
 // employee_id = employee ID
 // employee_mobile_number = Employee mobile number
+// first_Name = First Name
+// firstName = First Name
 func Humanize(s string) string {
 	return New(s).Humanize().String()
 }

humanize_test.go

@@ -15,6 +15,8 @@ func Test_Humanize(t *testing.T) {
 		{"employee_id", "Employee ID"},
 		{"employee_ID", "Employee ID"},
 		{"first_name", "First name"},
+		{"first_Name", "First Name"},
+		{"firstName", "First Name"},
 	}
 
 	for _, tt := range table {