Add additional error information to HTTP exceptions

[offa]

Adds additional information to the exception message (#208, #161).

Request failed: (400) Bad Request

becomes

Request failed: (400) Bad Request (message: {"error":"partial write: field
type conflict: input field "value" on measurement "x" is type string,
already exists as type integer dropped=1"}
)

[offa]

/cc @Globostofo

[offa]

ping @Globostofo

[Globostofo]

It does the job perfectly and simply!
Thanks for your consideration :^)