Redesign tags / fields API of Point

[offa]

Redesign the tags and fields API of Point.

• Introduce type (or typedef) for Tag and Field sets
• Replace Point::getTags() return type (deprecate in previous version)
• Replace Point::getFields() return type (deprecate in previous version)
• Query parsing might need unescaping
• Announce Point getter changes #183 (v0.7.x)

Candidates

• Insert float casted to double add noise to field #210

Related: #179