Kill off some usages of c_str.

Also changes some function params, but this is ok.
Some simplifications were also able to be made (ie. killing off strcmps with ==, etc).

Source/Core/Common/StringUtil.h

@@ -76,7 +76,7 @@ static bool TryParse(const std::string &str, N *const output)
 }
 
 // TODO: kill this
-bool AsciiToHex(const char* _szValue, u32& result);
+bool AsciiToHex(const std::string& _szValue, u32& result);
 
 std::string TabsToSpaces(int tab_size, const std::string &in);