Manage `GET_PIP_URL` value at single place for readability.

Add template for issues and pull requests

revisited

revisited

Unset `PIP_VERSION` before invoking `get-pip.py` as a workaround for `invalid truth value` error

Support for ActivePython

Ignore empty `.ruby-version` files

Command `rbenv version-name > .ruby-version` will create an empty `.ruby-version` file
before running `rbenv-version-file`. This causes `rbenv-version-file` to return empty
string which in turn causes `rbenv-version-name` to return `system`.

Ensure size of `.ruby-version` is non-zero as a workaround.

Use Markdown image markup in README

This also fixes the aspect ratio of the image being incorrect.

python-build: add anaconda[23]-5.1.0

Correct CPython 3.4.8 Checksums

The current checksums for tar.xz and .tgz files are reversed. This
causes python-build to fail with a checksum mismatch error.

Reversing the checksums to allow the build to succeed.

Improve screenshot in readme

Python-build updates

Push 3.7-dev to `3.7` branch

Add CPython 3.5.5

Add pypy3 5.10.1

Do not create `clear` shim when Anaconda is installed

Add `clear` to the Anaconda's default blacklist in order to prevent
pyenv from creating the shim script for it.

The `clear` command executable began included from Anaconda 5.0.0
onwards, and this executable now conceals that of the user's base system
- this hinders the user from running the `clear` command with the
`command not found` error output if a user installs and selects one or
more Python version(s) other than Anaconda 5.x.x.

Adding this one-liner to the blacklist allows the user to use the
`clear` command even when Anaconda 5.x.x is not selected by pyenv.

Allow binary installs of PyPy on Xenial

Add PyPy[23] 5.10

closes #1061

Add CPython 3.6.4 and remove 3.6.4rc1

Fix pyenv install on Solaris / Illumos