**Suggested by @cbeams:**
_includes/ref_block_chain.md:
* Mention that coinbase is the first transaction in a block.
**Suggested by @gmaxwell:**
_includes/ref_core_rpcs-abcdefg.md:
* Mention that you need to unlock your wallet when you run out of
keys in the keypool.
* Remove erroneous assertion that txindex=1 would allow
`getreceivedbyaddress` to check balances of addresses not
belonging to this wallet.
_includes/ref_transactions.md:
* Clarify that OP_RETURN scripts aren't usually executed because
they always return false.
en/developer-reference.md
* Add a warning about using block chain or mempool data in
executable context.
* update to modern, supported Ruby 2.0 version
* update gems to current versions using Bundler
* make jekyll configs confirm to current version
* switch deb package dependencies to cross-platform rvm
* ignore bundled dependencies
* some README mods as per @harding + @saivann
As suggested by @gmaxwell (thanks!), I tried to make clearer the benefit
of hardened keys:
* Described hardened keys as a solution in the first sentence of the
Hardened Keys subsection.
* Reordered the text so that the problem is described before the
solution, making the presence of a solution clearer.
* Added a prefatory sentence to the description of the two key
derivation formulas again describing the hardened formula as a
solution.
As suggested by @vbuterin (thanks!), I added a paragraph describing that
HD wallets don't use normal derivation on the master key so they don't
have an effective master public key. (See end of the diff.)
This is a fairly large diff because of the reordering, but no new
clauses were added besides those described above.
_includes/guide_wallets.md:
* Fix formula given for normal child key derivation to state that public
keys must also be provided to the HMAC hash function. This required
updating both text and images.
* Add one-paragraph warning about ancestor key compromise when the
ancestor extended public key is compromised along with a descended
private key. Update img/dev/en-hd-private-parent-to-private-child.*
to help illustrate this warning.
en/developer-reference.md:
* Remove %include% of previously-removed file which caused new versions
of Jekyll to die.
