[PATCH] Add support for Babel with Eshell, and some questions

[stardiviner <numbchild@gmail.com>]

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I added ob-eshell.el and documentation.

I got some questions:

When I run `make test`, found some babel languages are missing dependency.
What does that mean? and my ob-eshell is missing dependency too.

,----
| Code block evaluation complete.
|    passed  136/796  ob-vala/static-output (0.803677 sec)
|    failed  137/796  org-missing-dependency/test-ob-R (0.000377 sec)
|    failed  138/796  org-missing-dependency/test-ob-eshell (0.000403 sec)
|    failed  139/796  org-missing-dependency/test-ob-lua (0.000460 sec)
|    failed  140/796  org-missing-dependency/test-ob-maxima (0.000320 sec)
|    failed  141/796  org-missing-dependency/test-ob-plantuml (0.000304 sec)
|    failed  142/796  org-missing-dependency/test-ob-ruby (0.000354 sec)
|    failed  143/796  org-missing-dependency/test-ob-scheme (0.000307 sec)
|    failed  144/796  org-missing-dependency/test-ob-sqlite (0.000320 sec)
|    failed  145/796  org-missing-dependency/test-org-protocol (0.000304 sec)
|    passed  146/796  test-ob-exp/org-babel-exp-src-blocks/w-no-file (0.034372 sec)
|    passed  147/796  test-ob-exp/org-babel-exp-src-blocks/w-no-headers (0.031144 sec)
|    passed  148/796  test-ob-exp/org-babel-exp-src-blocks/w-no-headers2 (0.665415 sec)
`----

I have not found place for write doc for a specific Babel langauge for
ob-eshell under "* Languages" or other places. So I write document for
ob-eshell in Worg. Will push after this PATCH merged.

Question does all Babel languages document goes to Worg?

- --
[ stardiviner ] don't need to convince with trends.
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