Implement StringMap.IgnoreCase

[dragokas]

Please, add the option to be able ignore case sensitivity of StringMap key.

[Wend4r]

StringMap hash system may not provide for case insensitivity. It is possible to use when adding and reading elements using only lower or upper case

[KyleSanderson]

like most implementations we could tolower the keys, although that would result in unexpected behaviour on the keys.

Why is this desired? what's the use-case?

[dragokas]

Well, my case is using StringMap object to cache some stuff related to #phrases. Source Engine uses case insensitive look up for it, so I must mimic. At the moment I do CharToLower to store and retrieve StringMap values, but that's an additional performance consumption which could be done by setup new .IgnoreCase property of StringMap beforehand. I met other use-cases, but don't remember already.