A list of rippled version numbers, and the Github pull requests they contain.

0.28.0-b12: Includes pulls 836, 887, 902, 903 and 904.
0.28.0-b13: Includes pulls 906, 912, 913, 914 and 915.
0.28.0-b14: Includes pulls 907, 910, 922 and 923.
0.28.0-b15: Includes pulls 832, 870, 879, 883, 911, 916, 919, 920, 924, 925 and 928. FAILED pulls 909 and 926.