Merge branch 'release/0.4.2' into develop
added sources.cfg to git ignore
sourceloader now reads sources.cfg for source initialization
each source now receives a configuration dictionary
updated function description for __init__
changed __init__ of all sources to have an empty dictionary as default config value
ChemSpider now uses the token from sources.cfg with checks
created newresult function that uses the config for reliability
updated parse_extendedinfo to use the newresult function
updated parse_properties to use newresult function
created newresult function in NIST.py
updated parse_individidual_datapoints to use newresult function
updated parse_antoine_data to use newresult function
updated parse_generic_data to use newresult function
updated parse_transition_data to use newresult function
updated parse_aggregate_data to use newresult function
updated parse_generic_info to use newresult function
added config to NIST along with reliability check
chemspider __init__ now sets reliability to empty string if it does not exist in config
added config to wikipedia along with reliability check