Switch to MIT license (#158)

As far as I can tell, there are no significant contributions from non-Posit employees.

.Rbuildignore

@@ -13,3 +13,4 @@
 ^docs$
 ^pkgdown$
 ^vignettes/articles$
+^LICENSE\.md$

DESCRIPTION

@@ -11,7 +11,7 @@ Authors@R: c(
 Description: Enables the creation of object pools, which make it less
     computationally expensive to fetch a new object. Currently the only
     supported pooled objects are 'DBI' connections.
-License: GPL-3
+License: MIT + file LICENSE
 URL: https://github.com/rstudio/pool, http://rstudio.github.io/pool/
 BugReports: https://github.com/rstudio/pool/issues
 Depends:

LICENSE

@@ -0,0 +1,2 @@
+YEAR: 2023
+COPYRIGHT HOLDER: pool authors

LICENSE.md

@@ -0,0 +1,21 @@
+# MIT License
+
+Copyright (c) 2023 pool authors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

NEWS.md

@@ -1,5 +1,7 @@
 # pool (development version)
 
+* Pool has been re-licensed to MIT (#158).
+
 * `dbPool()` gains an `onCreate` parameter that allows you do something to
   every connection that pool creates. This is useful for setting options that
   you want to apply to every connection (#98).