Refactored code

Hi !
I refactored the code, adding functions, making other ones deprecated (but keeping support), and made the interface a bit more consistent (across function names, e.g. readKey:AsString, but readKey:intoNumber).
I made some functions private, and added an underline to distinguish them.
Here are the details : 
* Renamed and made private IOService functions (_smcOpen, _smcClose, _smcCall)
* Helper functions (_strtoul, _ultostr) are private too
* Deprecated : 
  * SMCReadKey:outputValue (replaced by _smcReadKey:toValue:)
  * SMCCall:forKeyData:outputKeyDataIn (by _smcCall:forKeyData:toKeyData )
  * getStringRepresentation:forSize:ofType:inBuffer (became stringRepresentationForBytes:withSize:ofType:inBuffer:)
  * readKey:AsString: (by readKey:IntoString) *not sure about this one, tell me how you feel*
* Added :
  * ``` -(UInt32) _smcIndexCount;```
  * ```-(BOOL) dumpToValueDict:(NSMutableDictionary**)valDict andTypeDict:(NSMutableDictionary**)typeDict;```
  * ```-(SMCVal_t) createEmptyValue;```
  * ```-(BOOL) readKey:(NSString *)key intoVal:(SMCVal_t *)val;```
  * ```-(BOOL) stringRepresentationForBytes: (SMCBytes_t)bytes
							withSize: (UInt32)dataSize
							  ofType: (UInt32Char_t)dataType
							inBuffer: (char *)str;```
  * ```-(BOOL) stringRepresentationForBytes: (SMCBytes_t)bytes
							withSize: (UInt32)dataSize
							  ofType: (UInt32Char_t)dataType
						  toNSString: (NSString**)abri;```
  * ```-(BOOL) stringRepresentationOfVal:(SMCVal_t)val
						 inBuffer: (char *)str;```
  * ```-(BOOL) stringRepresentationOfVal:(SMCVal_t)val
					   toNSString:(NSString**)abri;```
Nope, I didn't wrote this... Took it from @jedda work :
https://github.com/jedda/smc_util/blob/master/smc_util.c