Add .gitignore file

Used the C template from https://github.com/github/gitignore
Fix build under Postgres 9.3

With the change to the `.SECONDARY` rule in [this commit][1], vanilla
Postgres extension builds do not keep intermediate files.

Rather than directly defining `all` and `clean` targets, we should be
following the [Postgres guidelines for making extensions][2] if at all
possible. This is as simple as defining special variables before in-
cluding the PGXS Makefile and making sure all relevant dependencies can
be built if needed.

[1]: postgres/postgres@1eb1dde
[2]: http://www.postgresql.org/docs/current/static/extend-pgxs.html
Merge pull request #12 from citusdata/feature/9.3_build_fixes

Fix build under Postgres 9.3

cr: @metdos
(1) Added support for PostgreSQL 9.3. (2) README file is updated accordingly.
Merge pull request #14 from citusdata/feature/9.3_include_fix

Make mongo_fdw compatible with PostgreSQL 9.3.

cr: @jasonmp85
Add Markdown suffix to `README`

For better markup capabilities.
Enhance `README` markup

Links, lists, headers, etc.
Update license information

We mean to use LGPLv3, not GPLv3. The former allows a shared library to
be linked from non-free software; the latter does not.

Also updated copyright declarations (first year of release through
current release year).
Remove contact email

Users should open GitHub issues to report bugs.
Add guidelines for contributors
Add support policy

To set expectations.
Small wording/formatting changes to README
Return email to README

Per @ozgune's request.
Merge pull request #15 from citusdata/feature/update_docs

Update project documentation
Merge pull request #16 from citusdata/develop

MongoDB FDW for PostgreSQL 9.3