Add support for multiple simultaneous database features by using macros.

Diesel requires the following changes:
- Separate connection and pool types per connection, the generate_connections! macro generates an enum with a variant per db type
- Separate migrations and schemas, these were always imported as one type depending on db feature, now they are all imported under different module names
- Separate model objects per connection, the db_object! macro generates one object for each connection with the diesel macros, a generic object, and methods to convert between the connection-specific and the generic ones
- Separate connection queries, the db_run! macro allows writing only one that gets compiled for all databases or multiple ones

Cargo.lock

@@ -152,6 +152,7 @@ dependencies = [
  "oath",
  "once_cell",
  "openssl",
+ "paste",
  "percent-encoding 2.1.0",
  "rand 0.7.3",
  "regex",
@@ -274,9 +275,9 @@ dependencies = [
 
 [[package]]
 name = "chrono"
-version = "0.4.13"
+version = "0.4.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c74d84029116787153e02106bf53e66828452a4b325cc8652b788b5967c0a0b6"
+checksum = "942f72db697d8767c22d46a598e01f2d3b475501ea43d0db4f16d90259182d0b"
 dependencies = [
  "num-integer",
  "num-traits",
@@ -295,9 +296,9 @@ dependencies = [
 
 [[package]]
 name = "clap"
-version = "2.33.2"
+version = "2.33.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "10040cdf04294b565d9e0319955430099ec3813a64c952b86a41200ad714ae48"
+checksum = "37e58ac78573c40708d45522f0d80fa2f01cc4f9b4e2bf749807255454312002"
 dependencies = [
  "ansi_term",
  "atty",
@@ -781,14 +782,14 @@ dependencies = [
 
 [[package]]
 name = "handlebars"
-version = "3.3.0"
+version = "3.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "86dbc8a0746b08f363d2e00da48e6c9ceb75c198ac692d2715fcbb5bee74c87d"
+checksum = "5deefd4816fb852b1ff3cb48f6c41da67be2d0e1d20b26a7a3b076da11f064b1"
 dependencies = [
  "log 0.4.11",
  "pest",
  "pest_derive",
- "quick-error",
+ "quick-error 2.0.0",
  "serde",
  "serde_json",
  "walkdir",
@@ -1360,7 +1361,7 @@ dependencies = [
  "log 0.4.11",
  "mime 0.3.16",
  "mime_guess",
- "quick-error",
+ "quick-error 1.2.3",
  "rand 0.6.5",
  "safemem",
  "tempfile",
@@ -1519,9 +1520,9 @@ checksum = "1ab52be62400ca80aa00285d25253d7f7c437b7375c4de678f5405d3afe82ca5"
 
 [[package]]
 name = "once_cell"
-version = "1.4.0"
+version = "1.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0b631f7e854af39a1739f401cf34a8a013dfe09eac4fa4dba91e9768bd28168d"
+checksum = "260e51e7efe62b592207e9e13a68e43692a7a279171d6ba57abd208bf23645ad"
 
 [[package]]
 name = "opaque-debug"
@@ -1628,6 +1629,12 @@ dependencies = [
  "regex",
 ]
 
+[[package]]
+name = "paste"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f6ddc8e145de01d9180ac7b78b9676f95a9c2447f6a88b2c2a04702211bc5d71"
+
 [[package]]
 name = "pear"
 version = "0.1.4"
@@ -1873,6 +1880,12 @@ version = "1.2.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a1d01941d82fa2ab50be1e79e6714289dd7cde78eba4c074bc5a4374f650dfe0"
 
+[[package]]
+name = "quick-error"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ac73b1112776fc109b2e61909bc46c7e1bf0d7f690ffb1676553acce16d5cda"
+
 [[package]]
 name = "quote"
 version = "0.6.13"