'Create fetcher that validates certificates using selected
platform.
@param platform: platform name to use for TLS cert verification
@param certPlatforms: CertificatePlatforms instance with caPaths
for known platforms
@param ruleTrie: rules.RuleTrie to apply on URLs for following.
Set to None if redirects should not be rewritten'

def __init__(self, platform, certPlatforms, fetchOptions, ruleTrie=None):

    self.platformPath = certPlatforms.getCAPath(platform)
    self.certPlatforms = certPlatforms
    self.options = fetchOptions
    self.ruleTrie = ruleTrie
