log errors in GetApiConfigs

There was no log output for errors and the 500 response message is really unspecific 
{"error": {"message": "BackendService.getApiConfigs Error"}}
Rewriting tests to leverage appengine/aetest package
Modify travis.yaml to run tests straight from goapp of the App Engine SDK
Correct args for goapp tool; make unzip silent.
Update readme to mention we're testing with goapp tool now
Rewrite tests to leverage appengine/aetest of the SDK.
Alternative way to get the package using goapp tool.

Closes #29
Add namespace support for endpoints.Context

Example:

```go
c := endpoints.NewContext(r)
namespacedContext := c.Namespace("newspace")
item := memcache.Get(namespacedContext, "key")
```

Closes #33
Merge pull request #30 from bashtian/patch-1

log errors in GetApiConfigs
Correct formatting of custom error responses.

Closes #34
Correctly handle anonynous structs
Sanity check for duplicate service methods.

API Descriptor generator will now return an error if a service
has either duplicate method names or (HTTP method + path) entries.

Fixes #26
Merge pull request #38 from crhym3/anonymous-struct

Correctly handle anonymously embedded structs.

Fixes #36.
Merge pull request #39 from crhym3/dup-method-path

Sanity check for duplicate service methods.

Closes #26
Allow override schema name

This change makes it possible to prefix a schema in case of name conflict.
Merge pull request #42 from crhym3/prefixed

Allow override schema name.
Closes #37
Go vet, golint; modify tests according to Golang conventions.

Although this is a breaking change, it's trivial and concerns only methods
renaming. For instance, endpoints.HandleHttp() is now endpoints.HandleHTTP().
Fix TestPrefixedSchemaName test to use a constant.

t.PkgPath() may be different in certain environments.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	endpoints/errors.go