Allow setting all Jinja env options

[jayvdb]

sometimes the default jinja syntax is inappropriate.
Need option to set all options of the jinja env.
https://github.com/zyguan/textpl/blob/master/render.py

targets:
  - output: foo
    template: foo.jj2
    options:
      ..
      block_end_string: '*))'
      ...

This could be used to add basic support for many template types.

[jayvdb]

@ayan-b, you want to try this one next?

[jayvdb]

e.g. #52 and #51 could be implemented with jinja options.

initially create a new engine when options are different.

We can have a separate issue about optimising by re-using engines with the same options.

[jayvdb]

(We could even use this instead of 'copy' by giving copy targets impossible jinja options, i.e. start/ends which never appear in any text.

[jayvdb]

P.s. yaml spec references can be used to avoid the options in the yaml being repetitive. There is no need to create a shorter syntax.

And the options attribute should be reusable for other template engines.

[chfw]

I support options and this will change the engine interface:

apply_template(..., options=None)

[ayan-b]

Assigning myself.

[chfw]

Here is my further thought. This change here customizes the jinja2 env, resulting slight different jinja2 template engine behavior. An additional fancy feature will be required:

define:
  my_new_engine:  # create a reusable engine within this context
    - overrides: jinja2
    - options:
      ..
      block_end_string: '*))'
      ... 
targets
  - a.output: a.my_new_engine
  - output: b.output
    template: b.unknown
    template_type: my_new_engine
  - output: c.output  # this will create ad-hoc jinja2 engine, and get dumped after the op.
     template: c.alien
     template_type:
      - overrides: jinja2
      - options:
        ..
        block_end_string: '*))'
        ...
  - output: d.output
    template: d.unknown
    template_type: my_new_engine

In this way, the interface would be cleaner.