expose span options

[eli-jordan]

Fixes https://github.com/opentracing/opentracing-javascript/issues/93

The SpanOptions type is not exported from the module. This change simply adds an export to the index.ts file

[coveralls]

Coverage remained the same at 88.78% when pulling c3dc39a8e1efa48b53213ff1de4e5acdbb2fd472 on eli-jordan:expose-span-options into 1f32ae4aa77b866dce23ef6e33a3b9b08d458171 on opentracing:master.

[yurishkuro]

Could you also fix the tests? E.g. here the import should from the index, not from ../tracer, to ensure that these imports are not missed.

https://github.com/opentracing/opentracing-javascript/blob/master/src/test/opentracing_api.ts#L5

[eli-jordan]

@yurishkuro Done. I also updated mock_tracer._startSpan(...) to use the SpanOptions type

[coveralls]

Coverage remained the same at 88.78% when pulling 04eb5cba0a648b9dbd1babbdd680db44d8e369ec on eli-jordan:expose-span-options into 1f32ae4aa77b866dce23ef6e33a3b9b08d458171 on opentracing:master.

[coveralls]

Coverage increased (+0.3%) to 88.525% when pulling b17eac92ca63f2f4f53f997e89c291d2bc3980a0 on eli-jordan:expose-span-options into 1b32dfdede361d70978e7b41e4a381a5eb718de7 on opentracing:master.