Add support for expressions within template literals

[giuseppeg]

Fixes #25

[sarukuku]

🎉

[aga5tya]

👏

[giuseppeg]

@rauchg

Running 'styled-jsx Babel transform' from ~/code/styled-jsx/benchmark/babel.js ...
  basic x 123 ops/sec ±6.70% (61 runs sampled)
  with expressions x 93.34 ops/sec ±11.77% (52 runs sampled)

Passed:
  'basic' is etalon
  'with expressions' at 1.32x slower

Ran on a MacBook Pro (Mid 2014), 2.6 GHz Intel Core i5, 8 GB 1600 MHz DDR3

[TuckerWhitehouse]

Anything we can do to help get this merged?

[aga5tya]

Waiting on this 🍪

[rauchg]

@TuckerWhitehouse @aga5tya I'd like to understand why it's 30% slower, seems a bit much?

Also, @giuseppeg, what's the impact on an example that doesn't use expressions, before and after this patch?

[TuckerWhitehouse]

@rauchg what would be acceptable performance?

I ran the benchmarks locally, and these are my results:

master

Babel transform x 150 ops/sec ±3.40% (572 runs sampled)
'babel' from ~/Sites/styled-jsx/benchmark/babel.js (passed: 1, failed: 0)
  Passed:
    'Babel transform' is etalon

expressions

Running 'styled-jsx Babel transform' from ~/Sites/styled-jsx/benchmark/babel.js ...
  basic x 144 ops/sec ±4.52% (75 runs sampled)
  with expressions x 140 ops/sec ±3.97% (70 runs sampled)
'styled-jsx Babel transform' from ~/Sites/styled-jsx/benchmark/babel.js (passed: 2, failed: 0)
  Passed:
    'basic' is etalon
    'with expressions' at 1.03x slower

[TuckerWhitehouse]

Re-ran the benchmarks, and updated expressions to use a minimum of 500 samples.

master

Babel transform x 170 ops/sec ±1.50% (573 runs sampled)

expressions

basic x 168 ops/sec ±1.51% (567 runs sampled)
with expressions x 151 ops/sec ±1.32% (563 runs sampled)
  'with expressions' at 1.11x slower

[TuckerWhitehouse]

Thanks @rauchg, and nice work @giuseppeg!