Long initial init time

[felixmosh]

For the first usage of something from the lib, it takes ~10sec to load the proto.js file.
Simple report query like

await client.report({
    entity: 'campaign',
    attributes: [
      'campaign.id',
      'campaign.name',
      'campaign.labels',
      'campaign.advertising_channel_type',
      'campaign.advertising_channel_sub_type',
      'campaign.start_date',
      'campaign.end_date',
      'campaign.campaign_budget',
      'campaign.bidding_strategy',
      'campaign.bidding_strategy_type',
      'campaign.manual_cpc.enhanced_cpc_enabled',
      'campaign.network_settings.target_content_network',
      'campaign.network_settings.target_google_search',
      'campaign.network_settings.target_partner_search_network',
      'campaign.network_settings.target_search_network',
      'campaign.targeting_setting.target_restrictions',
    ],
    constraints: [{ key: 'campaign.id', op: 'IN', val: [].concat(campaignIds) }],
  })

Probably related to the fact that proto.js file is huge!

[hsource]

See #99 for a solution