Add gcp.Meta function, equivalent to aws.EC2Meta

This commit adds a new namespace and function: `gcp.Meta`, which can be
used to look up values from the GCP Instance Metadata service.

An example usage:

```
echo '{{ gcp.Meta "id" }}' | gomplate
```

This also supports paths, so usage like this works:

```
echo '{{ gcp.Meta "network-interfaces/0/ip" }}' | gomplate
```

1 files changed, 1 insertions, 0 deletions

diff --git a/funcs.go b/funcs.go
index e63c9872..2c7e70f1 100644
--- a/funcs.go
+++ b/funcs.go
@@ -12,6 +12,7 @@ func Funcs(d *data.Data) template.FuncMap {
 	f := template.FuncMap{}
 	funcs.AddDataFuncs(f, d)
 	funcs.AWSFuncs(f)
+	funcs.AddGCPFuncs(f)
 	funcs.AddBase64Funcs(f)
 	funcs.AddNetFuncs(f)
 	funcs.AddReFuncs(f)