Miner docs

[hanchon]

Closes: #477

Description

Miner RPC docs updated.
This PR also includes a fix to use the current configuration instead of the default when reading the configuration, to avoid overwriting the user configuration when saving the new gas price to disk.

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[hanchon]

Should I also update the Changelog file with this fix? More info on the issue #477

[fedekunze]

ACK thanks!

[fedekunze]

Should I also update the Changelog file with this fix? More info on the issue #477

@hanchon yes, if possible

[hanchon]

Should I also update the Changelog file with this fix? More info on the issue #477

@hanchon yes, if possible

Fix added to the Changelog