Possibly support one-sided bin limits

[GraemeWatt]

HEPData does not currently support open bin boundaries. It's not clear how these would be handled when exporting to ROOT and YODA formats. We'd also need to modify the HEPData plotting code to automatically choose an appropriate x-axis upper limit and show something like an arrow to indicate the open bin boundary. We could possibly consider an implementation if open bin boundaries were supported by ROOT/YODA, but for now it's not a planned feature. Note that the YAML specification of floating-point numbers (http://yaml.org/type/float.html) supports infinity given as a regex [-+]?\.(inf|Inf|INF), but JSON doesn't support infinity as a number. The YAML format would therefore be something like {low: 250, high: .inf} converting the high value to a string for JSON.

The current workarounds are either to give a string {value: '> 250'} instead of low and high limits, or alternatively insert an artificial upper limit like {low: 250, high: 500} and explain in the table description that there is really no bin upper limit.

Originally posted by @GraemeWatt in HEPData/hepdata_lib#167 (comment)

[GraemeWatt]

@yimuchen : I've bumped the priority of this issue, partially addressed it in 5a372ec, and opened HEPData/hepdata-converter#55 following your recent feedback.