Support reading remote AVC version files

[dbent]

@pjf @techman83 @BobPalmer
cc: @plague006 @politas @Dazpoet

This PR modifies the AvcTransformer to support reading remote version files. Apparently the last few versions of the AVC addon have supported using the remote .version file to determine compatibility in preference to the local .version file, if the remote .version file specifies the same mod version as the local .version file. This PR provides the same behavior.

This should bump the compatibility of CommunityResourcePack as the download specifies a maximum compatibility of KSP 1.1.1 whereas the remote specifies as maximum compatibility of KSP 1.1.2.

This .netkan

{
    "spec_version" : "v1.16",
    "identifier" : "CommunityResourcePack",
    "$kref" : "#/ckan/netkan/https://raw.githubusercontent.com/BobPalmer/CKAN/master/CommunityResourcePack.netkan",
    "x_netkan_license_ok": true
}

Produces the following .ckan.

{
    "spec_version": "v1.16",
    "identifier": "CommunityResourcePack",
    "name": "Community Resource Pack",
    "abstract": "Common resources for KSP mods",
    "author": "RoverDude",
    "license": "CC-BY-NC-SA-4.0",
    "release_status": "stable",
    "resources": {
        "homepage": "http://forum.kerbalspaceprogram.com/index.php?/topic/83007-105",
        "repository": "https://github.com/BobPalmer/CommunityResourcePack"
    },
    "version": "0.5.1.0",
    "ksp_version_min": "1.0.0",
    "ksp_version_max": "1.1.2",
    "conflicts": [
        {
            "name": "Kerbalism"
        }
    ],
    "install": [
        {
            "file": "GameData/CommunityResourcePack",
            "install_to": "GameData"
        }
    ],
    "download": "https://github.com/BobPalmer/CommunityResourcePack/releases/download/0.5.1.0/CRP_0.5.1.0.zip",
    "download_size": 16098,
    "x_last_revision_by": "harryyoung",
    "x_generated_by": "netkan"
}

[techman83]

Awesome, LGTM!