Build using conventional paths instead of /opt/

[fpesari]

Right now zyn-fusion builds in /opt/ but it'd be nice if it used the traditional paths (such as /usr/bin, /usr/lib and /usr/share) instead of /opt/ (which I know is also in the FHS, but is very uncommon outside of nonfree software).

Basically, this concerns the directories created in package/ when make pack is run (except completions), which are:

• font
• qml
• schema

I poked around zest a bit and I noticed that some functions use a search parameter or something along those lines to allow a different path than the current directory, for example,

# font/
def init_font
        search   = @search_path
        search ||= ""
        font_error = false
        sans = [search + "font/Roboto-Regular.ttf", "deps/nanovg/example/Roboto-Regular.ttf"]
...

# qml/
def loadIR(search=nil)
    l = Parser.new
    qml_data = nil
    if(search.nil?)
        qml_data = [
            Dir.glob("../mruby-zest/mrblib/*.qml"),
            Dir.glob("../mruby-zest/qml/*.qml"),
            Dir.glob("../mruby-zest/test/*.qml"),
            Dir.glob("../mruby-qml-spawn/test/*.qml"),
            Dir.glob("../mruby-zest/example/*.qml"),
            Dir.glob("src/mruby-zest/mrblib/*.qml"),
            Dir.glob("src/mruby-zest/qml/*.qml"),
            Dir.glob("src/mruby-zest/test/*.qml"),
            Dir.glob("src/mruby-qml-spawn/test/*.qml"),
            Dir.glob("src/mruby-zest/example/*.qml"),
            Dir.glob("qml/*.qml")
        ].flatten
    else
        qml_data = [Dir.glob(search+"qml/*.qml")].flatten
...

// schema/
void parse_schema(const char *json, schema_t *sch);
schema_t br_get_schema(bridge_t *br, uri_t uri)
{
    (void) uri;
    schema_t sch;

    //printf("[debug] loading json file\n");
    FILE *f = fopen("schema/test.json", "r");
    if(!f && br->search_path) {
        char tmp[256];
        snprintf(tmp, sizeof(tmp), "%s%s", br->search_path, "schema/test.json");
        f = fopen(tmp, "r");
    }
...

it'd be nice to be able to pass a variable to make which sets the path to one specified by the user, or to use $XDG_DATA_HOME by default (since all of those are architecture-independent files).