[BUG] Routing couldn't distinguish slashes even though I have the right regexp

**Describe the bug**

I want to combine multiple routes with slashes into a single parameter, like `/*/suffix` or `/**/suffix`, and `/a/suffix`, `ab/cd/suffix`, `a1/b2/c3/d-4/suffix` can match the rule, but it seems iris couldn't do this now (`path` is not suitable because I have other suffix like `/a/b/c/suffix/another-suffix/and-more-suffix`).

So, I wrote a regexp, and registered a custom macros, like this:

```go
regex := regexp.MustCompile("^[a-z0-9/-]+$")
app.Macros().Get("string").RegisterFunc("name", regex.MatchString)

assert.True(t, regex.MatchString("abc/def/ghi"))
```

I thought this would work, and `/ab/cd/ef/anything-else` could match `/{name:string name()}/anything-alse`, but actually, it didn't!

It seems that al slashes couldn't combine to a single param, maybe except `path`.

Could you please tell me how to implement my requirement above? I am puzzled now..

**To Reproduce**
Steps to reproduce the behavior:
1. register a custom macros:

```go
regex := regexp.MustCompile("^[a-z0-9/-]+$")
app.Macros().Get("string").RegisterFunc("name", regex.MatchString)
```

2. register a routing:

```go
app.Get("/{name:string name()}/balabala", helloWorldHandler)
```

3. try to get

```
curl localhost:8080/a/b/c/balabala
Not Found
```

**Expected behavior**

```go
curl localhost:8080/a/b/c/balabala
hello, world!

```

and we could get the param `name`:

```go
ctx.Params().Get("name") // "a/b/c"
```

**Desktop (please complete the following information):**
- OS: Ubuntu 18.04.LTS
- Go: go version go1.15 linux/amd64

**iris.Version**
- v12.1.9-0.20200814001959-6fee09f11ed1