Add sdk version to contract meta automatically

[leighmcculloch]

What

Add rust version and sdk version to contract meta automatically.

Rustc version is stored in meta under the key rsver.

SDK version is stored in meta under the key rssdkver.

Section `contractmetav0` (100 bytes):
Length: 100 (0x64) bytes
0000:   00 00 00 00  00 00 00 05  72 73 76 65  72 00 00 00   ........rsver...
0010:   00 00 00 06  31 2e 37 30  2e 30 00 00  00 00 00 00   ....1.70.0......
0020:   00 00 00 08  72 73 73 64  6b 76 65 72  00 00 00 34   ....rssdkver...4
0030:   30 2e 38 2e  34 23 32 62  33 30 65 34  37 33 36 36   0.8.4#2b30e47366
0040:   39 66 61 63  38 30 33 31  38 38 66 61  63 30 32 63   9fac803188fac02c
0050:   62 63 66 61  36 30 39 63  31 39 64 63  63 36 2d 64   bcfa609c19dcc6-d
0060:   69 72 74 79                                          irty

Why

The rustc version is a primitive for future supporting reproducible builds.

The SDK version is for debugging situations where incompatibilities arise across different versions, and for better understanding them.

Close #735