Fix the module for BEMTREE template processing

[b0rey]

Example from .enb/make.js:

    examples.configure({
        ...
        engines: {
            bemtree: {
                tech: bemtreePath,
                options: {
                    sourceSuffixes: ['bemtree', 'bemtree.js'],
                    forceBaseTemplates: true,
                    exportName: 'BEMTREE',
                }
            },
            bemhtml: {
                tech: bemhtmlPath,
                options: {
                    sourceSuffixes: ['bemhtml', 'bemhtml.js'],
                    forceBaseTemplates: true,
                    engineOptions: { elemJsInstances : true },
                }
            },
        }
    ])

bemtree use level.blocks/block/block.tmpl-specs/*.data.js as an input data and outputted level.tmpl-specs/block/*.bemjson.js

In detail: https://web-standards.slack.com/conversation/C09NSHNK0/p1497176019177782

[tadatuta]

oh, looks like current version of stringify-object requires new version of node.js :(

but i think we can drop 0.10 and 0.12 here https://github.com/enb/enb-bem-tmpl-specs/blob/master/.travis.yml#L4 and run tests on 4, 6 and 8 now. will you please update .travis.yml so we can be sure that all tests pass?

[tadatuta]

And it'd be extreamly awesome if you can update README.md according to changes you made

[b0rey]

I think I can do this, but after the following patches for this module, which I am currently doing.

[b0rey]

@tadatuta I finished with this PR, can you check it?

[b0rey]

up

[tadatuta]

@b0rey thank you! 🎉