Enhancing input file flexibility

[hiroaki]

The current GPX::GPXFile.new requires an instance of the File class for the gpx_file option when specifying a file, but I think this should be a bit more flexible.
For instance, Issue #34 expects StringIO and Tempfile to be loaded, and I agree.

I have checked the source of Nokogiri::XML::Document.parse for this modification. As a result, I thought it would be better if the parameters of GPX::GPXFile.new were the same as the API of Nokogiri::XML::Document.parse, but for compatibility reasons, I concluded that the implementation as shown in this PR would be better.
Incidentally, the idea of respond_to?(:read) is exactly what Nokogiri::XML::Document.parse does.

Implementing this PR facilitates the following scenarios:

• Example: Reading from STDIN

$ cat tests/gpx_files/gpx10.gpx | ruby -Ilib -rgpx -e 'puts GPX::GPXFile.new(gpx_file: $stdin).tracks.first.name'

• Example: Reading from OpenURI (where URI.open returns a Tempfile)

$ ruby -Ilib -ropen-uri -rgpx -e 'puts GPX::GPXFile.new(gpx_file: URI.open("https://raw.githubusercontent.com/dougfales/gpx/v1.1.1/tests/gpx_files/gpx10.gpx")).tracks.first.name'

I especially wanted to use it in the pipeline from STDIN, as in the first example.

[niborg]

@hiroaki I'm just seeing this. This seems quite reasonable. I will evaluate in the next few days. Thank you for the contribution!

[niborg]

Thank you!