Add feature example: editable packages

[uilianries]

I've added an example based on workspace feature, as they walk together, I've followed the same lib x app idea

closes #42

[uilianries]

This PR is blocked by https://github.com/conan-io/examples/pull/45

[uilianries]

it failed due multi config example:

----Running------

> cmake --build '/Users/travis/build/conan-io/examples/features/multi_config/test_package/build/7336ebca55c566ecc6b383dffaf3ae6eb18d5225' '--' '-j2'

-----------------

Scanning dependencies of target example

[ 50%] Building CXX object CMakeFiles/example.dir/example.cpp.o
[100%] Linking CXX executable bin/example
[100%] Built target example
hello/0.0.1@user/testing (test package): Running test()

ERROR: hello/0.0.1@user/testing (test package): Error in test() method, line 19

    assert ("Hello World {}!".format(str(self.settings.build_type)) in output.getvalue()), output.getvalue()

[uilianries]

mysteriously, Travis worked after restarting that CI job.

[uilianries]

@danimtb @jgsogo all green!

[uilianries]

I want to update editable packages on Docs and use that example there. Something similar to workspace

[jgsogo]

I want to update editable packages on Docs and use that example there. Something similar to workspace

Ok, perfect! I was missing that bit of information

[uilianries]

The documentation now has an appropriated PR with the new example: https://github.com/conan-io/docs/pull/1567

This PR must be merged first, otherwise, the documentation will be pointing to an invalid example.

[jgsogo]

Looks like, we have been bitten by this https://github.com/ninja-build/ninja/issues/1599 😭