Several bugfixes and improvements, change from http.request to request

[dwettstein]

Hi

I merged several commits from the other forkers altogether. The commits include the following fixes, changes:

• Fix spelling mistake in package.json (Spelling mistake in package.json #8)
• Fix switched host, port => adapted from @zhuqling
• Change from http.request to request => adapted from @zhuqling
• Add endpoints for metricnames, tagnames, tagvalues and tags => adapted from @zlim
• Add tests for the endpoints above
• Improve error handling
• Change error messages to those of Wikipedia
• Add more error codes (204, 401, 403, 503)

[dwettstein]

Tests added for #7:

• datapoints/query/tags
• metricnames
• tagnames
• tagvalues