export interface speeds

[qybl]

This PR exports interface speeds, the map consists of the speeds we have in our org but is not exhaustive, other than adding all possible speeds I can't think of a better idea to solve this.

This fixes #27

[bjornryden]

Thanks for making this - it's very useful. I tried having a go at it myself, but fell a bit short in my go skills.

A few comments:

• Would it be possible to regexp out the integer and the string instead? Aggregated interfaces, for example, can come with all weird capacities, such as "3Gbps".
• Logical interfaces can also have the "bandwidth" setting which acts much in the same way as this, in regards to "number+string", however it becomes a "float+string", as setting bandwith to "1200" ends up as 1.200Kbps. This could be useful for some people, if they have services from ISPs that are capped in some way beyong the physical interface.

Personally, I really could use drawing both upload and download limits. For now I just use a silly txt-exporter for these values, as there's no way of setting asynchronous speed limits in the "bandwidth" section. I was thinking maybe it could be worth doing a regexp on the interface description, maybe even extracting labels automatically from this as well. Eg. "CircuitID=XXXXXXX;DL=1000;UL=100;CustomerID=YYYYYYY".