fix(parser): allow whitespace between function name and argument list

[npazosmendez]

function ('foo') does not parse. Whether a name starts a function call was decided by testing the byte immediately after it for (, so a name followed by whitespace parsed as a metric name instead.

graphite-web accepts both spellings. Its call is funcname + leftParen, and pyparsing skips whitespace before each element of an And:

https://github.com/graphite-project/graphite-web/blob/1.1.10/webapp/graphite/render/grammar_unsafe.py#L86-L95

The whitespace is consumed only when ( follows, so the non-call path returns its remainder unchanged.

---

See graphite web test showing a succesfull parse:

$ docker run -d --name gw -p 8080:80 graphiteapp/graphite-statsd >/dev/null && \
until curl -sf -o /dev/null "http://localhost:8080/render?target=x&format=json"; do sleep 2; done && \
curl -sG http://localhost:8080/render --data-urlencode "target=randomWalk ('a')" -d format=json -d from=-5min; echo; \
docker rm -f gw >/dev/null
[{"target": "a", "tags": {"name": "a"}, "datapoints": [[0, 1785872317], [-0.15573856844799938, 1785872377], [-0.38545492969748807, 1785872437], [-0.12892994452545037, 1785872497], [-0.5987020007736302, 1785872557]]}]