add strict option

[43081j]

Fixes #253.

Enables stricter parsing, in that only expressions using the specified
importName from the moduleName will be parsed.

// moduleName = some-module, importName = foo
import { foo, bar } from 'some-module';
foo`test`; // parsed
bar`test`; // parsed
foo.bleh`test`; // parsed
bar.bleh`test`; // parsed

// moduleName = some-module, importName = foo, strict = true
import { foo, bar } from 'some-module';
foo`test`; // parsed
bar`test`; // ignored
foo.bleh`test`; // parsed
bar.bleh`test`; // ignored

[coveralls]

Coverage remained the same at 100.0% when pulling d69ed56 on crispthinking:strict-option into 9293945 on styled-components:master.

[chinesedfan]

Clever new option. I like it.

[chinesedfan]

@43081j Just released 1.6.0. Thanks for your efforts and enjoy!