[#31] Use mkDGitRevision only in executables

Description

Problem: in the current state contract code (AbstractLedger and ManagedLedger) calls mkDGitRevision in the library component. There are two problems with that:

• New commits and rebuilds of morley-ledgers executable potentially wont trigger git revision update in the contracts.
• There is nowhere to get git revision from when morley-ledgers is used as a library.

Solution: introduce a new documentation section DGeneralInfoSection, which wraps git revision and potentially other things like contract author, and insert this section in the contract code. Then make a wrapper buildInstrDocWithGitRev which finds DGeneralInfoSection and patches it with git revision provided by the caller. It is expected to be called only from the executable.

Related issue(s)

Resolves #31 (closed)

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