HashiCorp Vault configuration provider implementation for Microsoft.Extensions.Configuration.

When this package is installed, it allows calling AddVault() as described below to tell the configuration builder to hydrate config values from Vault (as opposed to JSON files or environment variables).

var vaultUri = Environment.GetEnvironmentVariable("VAULT_ADDR");
var vaultAccessToken = Environment.GetEnvironmentVariable("VAULT_TOKEN");
var prefix = "MyApp"; // each application should use its own prefix, in general

var builder = new ConfigurationBuilder()
    .AddVault(vaultUri, vaultAccessToken, prefix);

• Moved code that interfaces with Vault from separate project into the main project, under Vault namespace
• Added change history to readme
• Some internal changes to naming to match Buildium's code standards