Support Julia 0.7

[Teo-ShaoWei]

This commit implements the latest syntax for Julia 0.7, and so might break on Julia 0.6 and before. If needs be, Compat can be used to assist in backward compatibility, or alternatively just break support for earlier Julia versions.

Changelog:-

• Update isdefined to include the containing module, which is compulsory.
• Replace the depreciated matchall with an implementation using eachmatch.
• Replace the depreciated chr2ind with an implementation using eachindex.
  Instead of doing index arithmetic on Unicode string which give incorrect result, use prevind and nextind.
• Replace the depreciated takebuf_string(s) with a String(take!(s)) call.
• Replace Base.Test with Test.
• Update replace to use a pair to indicate the replacement.
• Update parse of integer string to state the compulsory type to map to. For now, all numeric are assumed to be Float64 as further casting to specific integer types can be done from there. Similarly, casting to boolean is specified accordingly.
• Replace parse with Meta.parse when parsing code strings.
• Use logging functions @warn and @error. warn has been depreciated for @warn, and to standardise the logging we use @error too. This result in a SystemError thrown instead of an ErrorException.
• Update REQUIRE to use Julia 0.7.