Raise the version up to 1.5.0, add upgrade script

Fix issues found after the review

This rule executes pgindent with header files only.

Fix output precision limit for double values (issue #118)

pgSphere used its own setting (set_sphere_output_precision function)
to limit the output precision of double values, that could not be
greater than 15 significant digits (DBL_DIG). It introduced some
problems with dump/restore. PostgreSQL uses its own precision setting:
extra_float_digits. The PostgreSQL setting allows to use more significant
digits.

This patch changes the default pgSphere output behaviour to utilize
PostgreSQL extra_float_digits. Now, extra_float_digits is used by default,
until set_sphere_output_precision is called.

The old behaviour is kept for compatibility purposes. Once,
set_sphere_output_precision is called, pgSphere starts to use the old
behaviour (read, please, issue #118 discussion).

The patch introduces a new function - reset_sphere_output_precision.
It is used to reset to the PostgreSQL behaviour after using
set_sphere_output_precision.

* Update upgrade script (reset_sphere_output_precision function)

* Add test for pgSphere output precision with different settings

expected/output_precision.out   - PG 10-11
expected/output_precision_1.out - PG 12+

* Add extra_float_digits = 2 for epochprop and bounding_box_gist tests

The upgrade script misses the altering of spoint operator family
to add operator 17. It is required for k-NN search.

Change the version to 1.5.1.