Saint John's -> St Johns
Yellow Knife -> Yellowknife

Done to prevent exceptions raised in python 3.6 environment.

Added a class to create error messages and wrapped parse, fetch,
and format_data in try/except statement to catch raised exceptions
and generate error pages.

Also, made changes based on PR revision requests.

Added base class for exceptions and continued work on parsing and
fetching methods.

Need to add more unit tests. Working on usgs/geomag-algorithms#162.

added a raise exception for more than 1 channel in configure

averaged data

Discovered a small typo in the BLC (Baker Lake) entry. Fixed it.

Only the BOU observatory had updated DECBAS values. This commit includes all DECBAS values adopted on July 1 2013, which estimated from the 2011 annual means. These values have been used in the preliminary data exported to Intermagnet since they were adopted, but they have not been used in geomag-algorithms.

fixed indentation

Previously, if l0 was None, we tried to calculate a default initial level. This was
problematic if yobs had no valid points from which to calculate a mean. Now, if yobs
has no valid points, default to l0=0. This is a bit arbitrary, but it is necessary
to prevent a NaN-valued l from being passed back out. Other defaults are equally
arbitrary.

Also, I noticed that the `s` variable was getting converted from a NumPy array to a
list just before the method returned. For consistency with other outputs, we no
longer convert, and just return a NumPy array.

I'm not sure this is functionally different from what there was previously. Is this what you were suggesting in your comment on this PR @jmfee?