Added option to create the file if it doesn't exist

Using AutoExecConfig_SetCreateFile one can specify if the config file
should be created if it doesn't exist yet.
There's header comment writting like SourceMod's AutoExecConfig does
including the plugin filename the cvars belong to.
You can set the filename to a different file by using the
AutoExecConfig_SetPlugin stock
Merge pull request #1 from peace-maker/master