customize open/close tags via 'string-template/custom'

[nenj]

The main module is now exposing two methods, 'process' (formerly 'template') and 'setOpenCloseTags'
The one-function structure of module.exports is thus changed, maybe requiring a version increment...
As you consider best, Matt.

[coveralls]

Coverage decreased (-2.04%) when pulling eadd4de on nenj:master into 8f28bb1 on Matt-Esch:master.

[Matt-Esch]

I think it is good to be able to set the tags, but it probably should not be exposed like this. I suggest that we keep the same default expectation i.e. index.js exports a format function which defaults to '{' and '}'. Then maybe you can require string-template/custom to expose the tag options. index.js would rely on this underlying implementation.

[coveralls]

Coverage remained the same when pulling edba0b9 on nenj:master into 8f28bb1 on Matt-Esch:master.