Add version functions to LFE

[oubiwann]

Fixes #297.

Add support for a version function as well as other "system info" functions. Tasks:

• provide Erlang, LFE, OS, and tools version info
• allow users to only provide the version of a single entry, if they so wish
• use an extensible and backwards compatible data structure (property list)
• provide convenience macros for use by developers in the REPL (e.g., (version) and (version 'app-nam))
• ensure new functions are accessible from any LFE module
• cache expensive calls
  • memoize where sensible to mitigate expensive system calls
  • refactor memoization to instead use the processes table (see @rvirding's comment below)
• add documentation
  • update lfe_shell.md
  • update lfe.1.md

Bonus tasks:

• add missing docs for Common Lisp module

[oubiwann]

I've updated the docs with formatting fixes.

[oubiwann]

@rvirding Is there any chance we could get this into the 1.2.1 release? I've been dying for this version function in LFE for ages ... it would be nice to clean up all the duplicate version-getting code in all the different LFE libraries ...

[yurrriq]

👍 I'd like to see (or write myself) a patch for #286 in 1.2.1 as well.

[rvirding]

I have a few comments:

• I don't think we should add a macro for version/0/1, no need for it.
• Should it be stored in each process dictionary? An alternative would be to keep it in an ets table owned by the init process with a global name, lfe-version-info.
• Shouldn't all the otp versions have the same format, not "R16B3" and "19.1"? Would make comparisons easier.
• Could generate LFE version at compile time and use that in code.

[rvirding]

If you were to add some docs in lfe_shell and the lfe.1.md file I would not complain. ;-)

[oubiwann]

@rvirding regarding version macros:

I'd like to be able to call (version) and (version 'appname) from the REPL. This is a common use case in other language REPL/shells and have found it to be quite a nice convenience. In our case, we do get the version number in the banner for LFE itself, but it would still be nice to have a short command to use for getting versions of other applications as well.

[oubiwann]

Will rebase and address the review feedback ...

[oubiwann]

I've updated to rebase off of the LFE 2.0 code base in develop.