TBR: docs: syncbase: s/yncGroup/yncgroup/

With this change, we establish a convention of treating
"syncgroup" as a single, common (non-proper) noun.

The main motivation for this change was consistency, for
a term that's used widely across our codebase and docs.

Arguments for "Syncgroup" over "SyncGroup" were:
- it's "Syncbase", not "SyncBase"
- we'd probably like to use "syncgroup" rather than
"sync_group" in snake-case text, e.g. in filenames like
"syncgroup_test.go"; using "SyncGroup" for camel-case
text would make these two inconsistent (Nick pointed
this out)
- avoids ambiguity about capitalization at the start of a
sentence vs. inside a sentence ("SyncGroup" vs.
"syncgroup"?)

(Note, I discussed this change with Bindu, Raja, and Nick
before making it.)

I mainly used 'find -exec perl -pi -e' to prepare this
change, plus manual inspection and tweaks. The main
painful part was updating lots of comments in the Syncbase
implementation to use "syncgroup" instead of "Syncgroup"
where that was the intended usage.

MultiPart: 1/11

Change-Id: I8b04e74985f6007ce27d3e4f33548574decf7e98
diff --git a/tutorials/syncbase-user-guide.md b/tutorials/syncbase-user-guide.md
index 94edb1c..264e5d5 100644
--- a/tutorials/syncbase-user-guide.md
+++ b/tutorials/syncbase-user-guide.md
@@ -347,19 +347,19 @@
     // Assumes we've already created the hierarchy myapp/mydb/mytable.
     s := syncbase.NewService("/localhost:4002")
     d := s.App("myapp").NoSQLDatabase("mydb", nil)
-    sg := d.SyncGroup("/localhost:4002/%%sync/myapp/mydb/mysg")
-    sg.Create(ctx, wire.SyncGroupSpec{
+    sg := d.Syncgroup("/localhost:4002/%%sync/myapp/mydb/mysg")
+    sg.Create(ctx, wire.SyncgroupSpec{
       Description: "my syncgroup",
       Perms:       perms,
-      Prefixes:    []wire.SyncGroupPrefix{{TableName: "mytable", RowPrefix: "foo"}},
+      Prefixes:    []wire.SyncgroupPrefix{{TableName: "mytable", RowPrefix: "foo"}},
       MountTables: []string{"/ns.dev.v.io:8101"},
-    }, wire.SyncGroupMemberInfo{
+    }, wire.SyncgroupMemberInfo{
       SyncPriority: 8
     })
 
 The code below joins the syncgroup.
 
-    sg.Join(ctx, wire.SyncGroupMemberInfo{
+    sg.Join(ctx, wire.SyncgroupMemberInfo{
       SyncPriority: 8
     })