added brief paragraph in README directing to install instructions

[ci skip]
relaxed timer test assertions
relaxed timer assertion further
Added test to check download_file error type (issue pointed out by @kbarbary)
Fix attempt to access errno when the exception sometimes doesn't have it

Closes #808
changed test-running message to work better with affiliated packages
Added option to initialize a Quantity with a Quantity or sequence of Quantities
Added test of quantity initialization
Added docs example of creating a quantity with a sequence
Change Column arg order from (name, data,..) to (data, name, ..)
Update tests for Column arg swap
Update Table docs for Column arg swap
add latex for R_sun and L_sun, switch order with solRad
Add docs explanation of why multi-column assignment fails silently
Add new Table method _rebuild_table_column_views

Some table manipulations can corrupt the Column views of self._data.
This function will cleanly rebuild the columns and self.columns.  This
is now used in `add_row()`, `sort()`, and `reverse()`.  It should likely
be used for any method that modifies `self._data`.

This is exactly the code that had been at the end of `Table.add_row()`
but now written out in a more understandable fashion with a bunch of
comments to explain some of the subtleties that I had to rediscover.
switch sol* back to first in def_unit
Merge pull request #829 from taldcroft/table/bug-sort

Bug with Table sorting.  This also affected the reverse method.
Merge pull request #764 from taldcroft/table/multi-col-docs

Table: multi-column assignment fails silently.  Add documentation
to explain why this happens.
Fix HDF5 test to use name and data kwargs to init Column
Merge pull request #766 from pllim/timer-tests-fix

Relaxed utils.timer test assertions