Added string.guid() and string.isoDate()

Add string format checks for GUIDs and ISO 8601 date strings.

string.guid() will match the following format examples:

{D1A5279D-B27D-4CD4-A05E-EFDD53D08E8D}
{B59511BD6A5F4DF09ECF562A108D8A2E}
{5ba3bba3-729a-4717-88c1-b7c4b7ba80db}
{7e9081b59a6d4cc1a8c347f69fb4198d}
69593D62-71EA-4548-85E4-04FC71357423
677E2553DD4D43B09DA77414DB1EB8EA
0c74f13f-fa83-4c48-9b33-68921dd72463
b4b2fb69c6244e5eb0698e0c6ec66618


string.isoDate() will match the following format examples:

2013-06-07T14:21:46.295Z
2013-06-07T14:21:46.295+07:00
2013-06-07T14:21:46.295-07:00
2013-06-07T14:21:46Z
2013-06-07T14:21:46+07:00
2013-06-07T14:21:46-07:00
2013-06-07T14:21Z
2013-06-07T14:21+07:00
2013-06-07T14:21-07:00