Add RPC docs for older Bitcoin Core versions

[0xB10C]

As mentioned by @fanquake in #914 (comment), we might want to add RPC docs for some older Bitcoin Core versions. Comparing bitcoin/bitcoin tags with the docs available (< means missing):

0.8.0	      <
0.8.1	      <
0.8.2	      <
0.8.3	      <
0.8.4	      <
0.8.5	      <
0.8.6	      <
0.9.0	      <
0.9.1	      <
0.9.2	      <
0.9.2.1	      <
0.9.3	      <
0.9.4	      <
0.9.5	      <
0.10.0	      <
0.10.1	      <
0.10.2	      <
0.10.3	      <
0.10.4	      <
0.10.5	      <
0.11.0	      <
0.11.1	      <
0.11.2	      <
0.11.3	      <
0.12.0	      <
0.12.1	      <
0.13.0	      <
0.13.1	      <
0.13.2	      <
0.14.0	      <
0.14.1	      <
0.14.2	      <
0.14.3	      <
0.15.0	      <
0.15.0.1      <
0.15.1	      <
0.15.2	      <
0.16.0		0.16.0
0.16.1		0.16.1
0.16.2		0.16.2
0.16.3		0.16.3
0.17.0		0.17.0
0.17.0.1      <
0.17.1	      <
0.17.2	      <
0.18.0		0.18.0
0.18.1	      <
0.19.0		0.19.0
0.19.0.1      <
0.19.1	      <
0.19.2	      <
0.20.0		0.20.0
0.20.1	      <
0.20.2	      <
0.21.0		0.21.0
0.21.1	      <
0.21.2	      <
22.0.0		22.0.0
23.0.0	        23.0.0

To discuss:

• Should we add old docs? Do they provide value?
• How far back should we add RPC docs?
• Only major releases?

[0xB10C]

I'd be happy to pick up adding a few of these if there's agreement that this is something we think is valuable.

[0xB10C]

For reference, there's also #590

[katesalazar]

duplicate of #590, can close