Replace string parsing function from atol to StringToLong

int64_t on same architectures could be long int and on some others could be long long int
Merge pull request #347 from mhamrle/fix_convert_strings

Replace string parsing function from atol to StringToLong
rewrite OTData, new ot_data_t typedef
update OTCrypto to make use of new OTData
update OTASCIIArmor to make use of new OTData
update OTEnvelope to make use of new OTData
update OTSymmetricKey to make use of new OTData
headers updated to make use of new OTData
updated OTAsymmetricKey to make use of new OTData
updated ot core to make use of new OTData
udpated remaining ot to make use of new OTData