SSL support for mongodb erlang driver

Hi,

I've added SSL support. The code is working but as you may see: I'm not an erlang expert. 
Anyway, I'd appreciate if you would take a look and tell me your comments or merge it ;)

In order to connect with SSL to the MongDB you need of course a mongodb with SSL compiled and those new functions:

```erlang
% SSL %
-spec ssl_connect(host()) -> {ok, connection()} | {error, reason()}.
%@doc Connect to given MongoDB server using SSL.
ssl_connect(Host) -> ssl_connect(Host, infinity, []).

-spec ssl_connect(host(), timeout()) -> {ok, connection()} | {error, reason()}.
%@doc Connect to given MongoDB server using SSL.
ssl_connect(Host, TimeoutMS) -> ssl_connect(Host, TimeoutMS, []).

-spec ssl_connect(host(), timeout(), ssl:ssloption()) -> {ok, connection()} | {error, reason()}.
%@doc Connect to given MongoDB server with SSL support.
ssl_connect(Host, TimeoutMS, Options) -> mongo_connect:ssl_connect(Host, TimeoutMS, Options).


-spec ssl_connect_factory (host()) -> resource_pool:factory(connection()).
%@doc Factory for use with a connection pool. See resource_pool module.
ssl_connect_factory (Host) -> ssl_connect_factory (Host, infinity, []).

-spec ssl_connect_factory (host(), timeout()) -> resource_pool:factory(connection()).
%@doc Factory for use with a connection pool. See resource_pool module.
ssl_connect_factory (Host, TimeoutMS) -> ssl_connect_factory (Host, TimeoutMS, []).

-spec ssl_connect_factory (host(), timeout(), ssl:ssloption()) -> resource_pool:factory(connection()).
%@doc Factory for use with a connection pool. See resource_pool module.
ssl_connect_factory (Host, TimeoutMS, Options) -> {Host, fun (H) -> ssl_connect (H, TimeoutMS, Options) end, fun disconnect/1, fun mongo_connect:is_closed/1}.


-spec ssl_rs_connect (replset()) -> rs_connection(). % IO
%@doc Create new cache of connections over SSL to replica set members starting with seed members. No connection attempted until rs_primary or rs_secondary_ok called.
ssl_rs_connect (Replset) -> mongo_replset:ssl_connect (Replset).

-spec ssl_rs_connect (replset(), timeout()) -> rs_connection(). % IO
%@doc Create new cache of connections over SSL to replica set members starting with seed members. No connection attempted until rs_primary or rs_secondary_ok called. Timeout used for initial connection and every query and safe write.
ssl_rs_connect (Replset, TimeoutMS) -> mongo_replset:ssl_connect (Replset, TimeoutMS).

-spec ssl_rs_connect (replset(), timeout(), ssl:ssloption()) -> rs_connection(). % IO
%@doc Create new cache of connections over SSL to replica set members starting with seed members. No connection attempted until rs_primary or rs_secondary_ok called. Timeout used for initial connection and every query and safe write.
ssl_rs_connect (Replset, TimeoutMS, Options) -> mongo_replset:ssl_connect (Replset, TimeoutMS, Options).


-spec ssl_rs_connect_factory (replset()) -> resource_pool:factory(rs_connection()).
%@doc Factory for use with a rs_connection pool over SSL. See resource_pool module.
ssl_rs_connect_factory (ReplSet) -> ssl_rs_connect_factory (ReplSet, infinity, []).

-spec ssl_rs_connect_factory (replset(), timeout()) -> resource_pool:factory(rs_connection()).
%@doc Factory for use with a rs_connection pool over SSL. See resource_pool module.
ssl_rs_connect_factory (ReplSet, TimeoutMS) -> ssl_rs_connect_factory (ReplSet, TimeoutMS, []).

-spec ssl_rs_connect_factory (replset(), timeout(), ssl:ssloption()) -> resource_pool:factory(rs_connection()).
%@doc Factory for use with a rs_connection pool over SSL. See resource_pool module.
ssl_rs_connect_factory (Replset, TimeoutMS, Options) -> {Replset, fun (RS) -> RC = ssl_rs_connect (RS, TimeoutMS, Options), {ok, RC} end, fun rs_disconnect/1, fun mongo_replset:is_closed/1}.
```

Thanks,
Michael